Your experience with the G85 is about what mine was, that camera is a big ole piece of junk, so please don't judge the GH5 based on your use of the G85. I have zero issues with AF on GH5, keep in mind they have done 4 or 5 firmware updates now, so if you look at any YouTube AF video, check the date, odds are they are on the old firmware. GH5 works perfectly for me. They are going to release yet another firmware update this moth, things only getting better in the GH5 world.
Another option to consider is the new GoPro Heo 7, just got this thing and so far it has exceeded every expectation, and for $299 its a steal. The stabilization is crazy good, picture /video quality is good, and the audio is surprisingly good, and for an extra $60 you can get the external mic hack that puts audio over the top. See for yourself.