That might be true for older versions—dunno.
Photoshop CC 2021 opens Fujifilm GFX100S files open just like Fujifilm GFX100 files.
Adobe has its bugs and I’ve reported on them many a time. But one thing Adobe does better than anything out there is to stay current with new camera releases. That is worth every penny to me, since I am constantly working with new cameras and lenses.
I consider $10/month a bargain for Photoshop/Lightroom. Compare that to my cell phone bill or the cost of my time for constant crap-grade macOS and iOS updates, and it’s a rounding error. Wasting my time doing in-camera conversion to TIF (which crashes the GFX100S very quickly) is a foolish alternative IMO, a loss on both workflow features and time. If you do so, then later you have to reproduce the conversion using the raw converter facilities, for guaranteed different results—this is a really bad tradeoff.