So far I’ve yet to encounter the separation between save and game data issue. It’s permissions that drive me up the wall. I’ve tried giving everyone write access, I’ve tried creating a group specifically for games. But no, proton/wine prefixes require ownership and not just access, and will not yield, and Steam won’t even show what’s the issue unless you run it from terminal.

This. It also made me genuinely hate how Steam on Linux handles library sharing on a multi user system.