IronFilm

What's your total budget? As a secondhand Panasonic GH5S (an older MFT camera, but damn good low light for its time! Note: this is a totally different sensor to the GH5! Don't mix them up) with a full set of f0.95 primes plus a couple of COB lights, couple of 1x1 panels, and a few LED tubes with of course all the stands/modifiers you wish, will cost a similar amount as a new Sony FX3 with a couple of zoom lens and nothing else. 
Yet that GH5S package will out perform by a large margin the FX3 when you're filming narrative shoots outdoors at night. 
 
As can most modern Super 35mm / APS-C cameras! Even good MFT cameras (GH5S / GH7 / P4K / E2-M4) can handle these tasks with ease. 
Even if your particular location you're using doesn't have any ambient light (or only a very small amount of it), you can still have the possibility of this ambient light existing to drive the motivation of your "artificial" lighting. Could there be a street lamp out of frame that's throwing light onto your subjects? Yes, so place a light there to emulate it. 
Your scene will look a lot better because of it when done right. 

Looking forward to hearing your thoughts on the S9 after you put it through its paces. I will be using mine in a similar use case and think it will be perfect. I've been missing my GX85 Street camera so happy to have something small and light to take around with some M lenses. 
V-Log and Stabilized FF 6k Anamorphic with Lidar autofocus on a mini $1,200 body. What a world we live in...

I’d buy it immediately if it cost 1000-1200€

I kind of think you should turn your question around: if you're shooting narrative films and short documentaries, you should be focusing on learning about lighting and buying the gear that will help you adequately light your scenes, rather than looking for a camera that can handle poor lighting conditions. People constantly focus their budget and attention on cameras and ignore lighting, which is backwards. Lighting is 95% of what makes an image "cinematic." Any camera can look good with good lighting.
Nowadays even a single "run and gun" operator can use portable lights; you don't need a crew, C-stands, etc. If I had to do it over again I'd spend 2 years learning how to do lighting before I even started thinking about which camera to get.
 

I remember those videos. He really led the early movement for minimal camera setups at the time. Very inspiring to me and my travel kits over the years.
I think about those old videos and also Kenny Ty and his early Canon T2i stuff on Vimeo whenever I get too fixated on camera specs or have late night GAS...
 

I remember being very impressed with what Brandon Li shot years ago with his Sony RX100 that he put up on vimeo:
https://vimeo.com/rungunshoot 
But I can't seem to find it again. 
He likely removed remove, like he did with his Sony NEX-5N videos (probably because of the people who were in them, and didn't want his brand image associated with them any longer):
https://web.archive.org/web/20130215084133/https://www.rungunshoot.com/the-350-docu-filmmaking-kit-depreciation-is-wonderful/ (ha, I see my old comment there from 2013! Forgot I wrote that)

True story;
 
Years ago I was hired to fly to Thailand and follow around the worlds leading Michael Jackson impersonator for a concert tour. If things went well I was going to be hired on to film the rest of the world tour. Everything was super last minute and I had just sold my camera so I ended up going totally minimalistic and grabbing the RX100. I had been using it as a B-Cam for a few months and was pretty comfortable with it but it was still terrifying coming from my rigged out 5Dmkii. 
At my stopover in Hawaii I learned that the Thai people were protesting and they were marching in the street, the economy was tanking and things were a mess. Concert was cancelled. Ended up flying to Nepal to film some other documentary stuff for a friend and his hemp company for two months. RX100 was a blast to use and I really enjoyed going so minimal up in the mountains. Next trip I bought the GH4 and GX85 (Based on Andrew's articles here) And the RX100 was quickly sold after seeing the image stabilization and the really filmic image of the little GX85 beast. 

Yes, I mean exactly that. It was my sole video camera for an entire season.
No full length ceremony or speeches etc, but hundreds of clips throughout the day.
I’ll go see if I can find anything on Vimeo but it might be a bit old now…!!

You might not have to what till next year,I'm shopping the Japanese websites and seeing some killer deals. At around $1,000 I think the S9 is an amazing deal. I'm going to scoop one up next paycheck and have some fun with it. I sold my GX85 a few months ago for a really solid price on eBay so it's getting close to an even swap for the S9 financially. I would love a new GX body with some of the GH7 love but that ship will probably never sail. The S9 is going to be the little brother to the S5iix and maybe a used S1R to round out my doc travel kit for a current project. 
If Lumix will end up removing record limits in firmware updates and give us a few more specs I feel like the Sigma FP crowd could even jump ship for the 6k open gate and ease of file codecs. 
 
No tax and cheap Fedex for $1,200 on Japanese sites today. Some even have the craptastic pancake lens included. 
 

This video is pretty out of date and doesn't take any of the new firmware updates into account. Firmware version 1.6 on 11/24/2020 added the "Secret Sauce"...
 
1. Improved AF performance
• Tracking and recognition performance of AF have been improved with an addition of head recognition.
• Human/Animal recognition can be set ON or OFF when the AF mode is set to [1-Area] or [1-Area+].
• [AF+MF] can be used during video recording.
 
2. Added video functions
• The following 5K(4992x3744) video recording mode in MOV format has been supported. - 5K30p/25p/24p, 4:2:0 10bit LongGOP, 200Mbps, LPCM
• [Like 2100(HLG)] has been added in [Photo Style] to support 10-bit HDR video recording.
• [Luminance Level] function supports the 10-bit mode.
• High-Resolution audio recording using an XLR Microphone Adaptor DMW-XLR1 is available and it can be controlled with [XLR Mic Adaptor Setting] menu. * MOV only
• 4K 60P/50P 4:2:2 10-bit video output over HDMI has been supported.
• [SS/Gain Operation] function has been added.
• [Red REC Frame Indicator] is available. • It is possible to play back vertical videos vertically. 

And then he went and did another 180 🤪
Went back and tried the S1H + battery grip + over 1kg lens and...just no.
I wanted to get away from that for very specific reasons.
I thought, maybe I could go back, but no, I just can't.
Well if I had to as in if there was no other choice, I could, but there are there options.
I've wrestled with it for a few days and in the end decided to stick with the original plan.
That is for video, I am covered. Not a single thing that I want or need. Rien, nada, nuffin.
It's the photo side where I have had the biggest issue, but other than the very occasional random lock up issue on the A7RV, it's just the best tool for me combined with the trinity of Tamron 20-40, 28-75 and 70-180.
I had to send the Samyang 35-150 back. It's just too big and heavy and that's just not for me anymore.
The arrival of the S9 also helped put things in perspective because although that is purely a video unit for me..and I am still waiting on the cage just to give it some grip really, it confirmed that smaller and lighter combos is my direction.
I also worked out a better way to make the 61mp A7RV work for me in that I chose it principally because it would give me the option to shoot uncompressed 61mp raw files for the max quality, but also at the turn of a dial, 26mp medium raw files which would be 85-90% of my work. Except no batch editing de-noise software will touch those files which is not something widely reported and unless you experience it and then go looking for the info...
Anyway, I have reset the thing for full uncompressed raw as a setting, compressed raw as another and uncompressed crop mode as a third and flitting between those 3 modes, will reduce my file and storage size to around 40% (compared with only having to use the full 61mp uncompressed).
Every time I think I've finally nailed it, there's something, but this time, I believe I have...
Lumix is now a 2.5 year old system for me and my only concern (very slight) is potential overheating on the S9, but I suspect that is going to be extremely unlikely based on my use case.
I've used the Sony on 3 jobs now and whilst I had a few teething issues, I think as with most tools, if you can get past a certain point, it becomes to come together. I think I just had to ride out that learning curve plus the medium raw thing was a big disappointment.
The thing that finally convinced me though was I had to go back to edit the final job I shot on 24mp Nikon and though those files are easier to work with SOOC, they are not on the same level as the 61mp Sony files ultimately.
Sorry for wasting everyone's time 😘

And now Meike has released an 85mm lens for L Mount:
 https://meikeglobal.com/products/meike-85mm-f1-4-auto-focus-lens?variant=45431946903780
Rather "expensive" at $499!!
Hopefully with time it will see a big price drop, and/or a cheaper f1.8 version

Every system needs a cheap nifty fifty! Either for the beginner starting out, or even just as a back up lens for someone more established. 
That was one of the issues with L Mount, their lenses are too high priced. But now one of those pieces of the jigsaw has been solved:
The Meike 50mm F1.8 Full Frame Auto Focus L-mount Lens (already available in Z Mount and E Mount)

https://meikeglobal.com/products/50mm-f1-8-auto-focus-lens-for-portrait-photography
 

But great news if you want a big built-in screen and minimal physical buttons...   the camera already exists and is fairly affordable, especially when on sale.
 
https://www.blackmagicdesign.com/products/blackmagicpocketcinemacamera

Cost and power consumption are definitely concerns.  Losing physical buttons and the dial is also not taking a step forward IMO. 

@zlfan trying not to hijack the R5II thread...
 
 
The final short film
 
 
 

My used FX30 is only slightly more expensive than brand new ZV-E10 II..
Used A6700 can be had for cheaper than ZV-E10 II in my country.
But they are for different market like you said, for me I defeinitely prefer used A6700 for best bang for the bucks, it got mechanical shutter and AI stuff which E10II lacks.

Well that went tits up...
First the fact that 26mp medium raw is not compatible with any current batch editing software which meant shooting everything at 61mp which was not the plan.
Then the thing keeps locking up. Or rather not switching on at random times forcing battery out, battery in, which is hardly ideal at key moments. It has happened now 2-3 times on each of the 3 shoots I have used it on. Not good enough.
Plus it just is not as good in low light as the Nikon Zf/Z6II or any of my 24mp Lumix cameras. It just isn't.
So I'm returning it and selling everything Nikon and Tamron.
For what?
My trusty fave camera of all time, my S1H which has a ridiculous trade in value of around €700.
OK, I need to buy a couple of lenses and I have to compromise on my stills camera set up going back to between 2.5/3kg in my hand, but it also puts €6k+ back into my account.
Lesson learned. L Mount is just the best system for me so I need to stop dicking about with any and everything else.
Samyang 35-150mm f2/2.8 arriving next week in time for my next shoot and Sigma 28-45mm f1.8 on preorder for my indoor and low light lens.
Oh well, I tried.
S9 arrives tomorrow and was going to replace one of the S5II's which in turn replaced the S1H which was going to be sold, but it's simply a case of repurpose the S1H back into being a stills camera, a role it has fulfilled before superbly. And will once again.
Maybe an S2R or S2H next year, but for the rest of this one, probably not.
S5II x2 in a static role for video + S9 run & gun + S1H stills. Done. For now...

I'll send them some angrily worded emails telling them off! 😉

I'll send them some angrily worded emails telling them off! 😉

Yes, and they are much distinct pieces of glass despite their same focal length:
 

Every system needs a cheap nifty fifty! Either for the beginner starting out, or even just as a back up lens for someone more established. 
That was one of the issues with L Mount, their lenses are too high priced. But now one of those pieces of the jigsaw has been solved:
The Meike 50mm F1.8 Full Frame Auto Focus L-mount Lens (already available in Z Mount and E Mount)

https://meikeglobal.com/products/50mm-f1-8-auto-focus-lens-for-portrait-photography
 

That's a pity you didn't put in a little extra effort to look further. There is one listed right now for only US$12K: https://www.ebay.com/itm/175568291816 
You missed out on a bargain! 

It's very expensive, but the Sonosax M2D2 is a small, extremely high-quality preamp that has two mini-XLR inputs. It outputs line-level stereo analog to a camera; it also outputs a digital signal via USB or AES. It has some of the best preamps and converters available anywhere. It's powered by one battery and can run for hours even with phantom power on both inputs. Sonosax doesn't sell a camera mount for it but you can download a 3D-printable file for one from their website. I use it mainly for music recording (I recorded our last album with it) but might use it for video one day.