It’s set to 0-1023. But I always record V-Log and I don’t know if that setting also affect V-Log really (which I assume would override that anyway to get full range… why would a camera shoot Log with video levels…well…who knows ).
Regarding the XT3 issue, it seemed to be hardware dependent also… my older iMac didn’t seem to mess up levels even with the same h265 clips… I remember that sh*t really frustrating me at some point. Also I think by Resolve 17 that issue was gone, have you had it with the latest Studio version ? I don’t have my Fuji anymore so I can’t check, or maybe with an older file.
But as you said, I’m absolutely convinced that people spent years editing Fuji files with the wrong levels clipping their highlight and crushing their shadows without even knowing it… which is a shame because the files are nice.