I’m pretty sure S1H has IBIS from talking to Panasonic rep, not a definitive yes, rather a ‘I can’t say but I’d expect so ?’ answer
I picked up an S1 for £1750 at a store open day, and free V Log! Awesome camera. I’m just using Voigtlander VM 35/1.2 at the moment. Amazed how good the IBIS is compared to A7iii
I prefer S1 to S1H I think, 10 bit 4K 30p will do me and the camera is smaller without the vents. To be fair, the 8 bit codec already looks superb, 10 bit is a bonus.