Sounds like there's something wrong somewhere — manual focus should work fine when recording on the GH5. It does on my GH5S, and I'm not aware of there being any published difference in that regard between those two bodies.I find the manual focusing to be perfectly acceptable. However, it won't change focus while recording.
The adapter feels ever so slightly loose on my GH5.
Dismounting the lens can be somewhat difficult, any advice to easily and safely remove it?
Which adapter did you end up getting?