Best way I know to test/describe the issue, is that if you have the camera set to raw only, and hit play, the embedded jpg that is shown when viewed at 100 percent is blown up too far, you can't tell critical focus at all. The first time I used the GFX in the field I was shocked as it seemed all the images were out of focus. This is coming from a P1 or Nikon camera usage. At first I just though that the GFX playback was over zooming, and used the two finger pinch on the screen to shrink it down. About 1/3 of the way. However you start to feel the effect of the image being too sharp. But I got to where I could determine what was in focus and used that method.
If you have the GFX set to write a raw to one card and full sized high quality jpg to 2nd card (with sharpening turned on 1 or 2) after you shoot, if you switch to 2nd card and look at the jpg, it's a full resolution jpg and much easier to determine critical focus. You can tell this because the image is larger on the display and not appearing to be blown up past 100%.
Nikon had a similar issue with the D800/D810, where default view was way past 100%, the D850 has this fixed with a setting for true 100% view. Same with Z7.
Phase One, has always had a perfect embedded jpg view of a 100% image, still by far the best in the field IMO.
Fuji takes a great shot, but they did not really put much thought into the playback IMO. Having to use 2 cards, 1 dedicated to jpgs for true viewing is not the best process and wastes a card. I never use jpgs from any camera so to me this process is not best practice.
I have reverted back to 2 cards, raw only, sequential, and just have gotten to where I can view the embedded jpg and figure out my critical focus.
BTW, Live View at 100% is also very hard to deal with (at least for me and many others) even with focus peaking on.
P1, I almost always manually focus as I never have liked the XF/DF+ AF system. Fuji, I almost always use AF, as it's tack on, and when it hits, you never have to check unless you are working a huge range of focus 2 feet to infinity. Fuji's AF in low light and low contrast scene is very hit and miss, more miss than hit. I had hoped to see a firmware improvement over the 2 years the camera has been around (almost 2 years) but AF has not been worked on. Working a scene with a GFX, early morning low light is very challenging, for manual focus is hard to determine and AF will more than likely not get a lock unless you can find something good light on it.
Paul C