It’s hardly mentioned anywhere, but an unknown update made it impossible for me to pose physbones on Quest, on anyone or myself. It’s not just my avatar’s settings: I uploaded an avatar months ago that I posed all the time for fun, then just recently I put on the same Avatar (haven’t updated it in ages) and poof, no longer poseable. According to one Discord comment, this occurred starting with the Hand Tracking update, but I myself cannot say exactly which update it happened. I have already tried reinstalling the game.
(Additional tests: PC users can pose my avatar’s physbones and I can release the pose via grab/release. I still cannot pose anything myself.)