Has it really been that long? Apparently so. Valve originally announced their rebranding of Steam Play with Proton back on August 21st, 2018. Seems like a good time for a quick reflection being halfway to a decade old now with the tech that gave rise to the Steam Deck.
Problem for me is def going to be modding games, have they fixed alt tabbing between games and desktop yet at least? It used to “crash” the game for me if I tabbed out even for a second.
I’ve never had this issue but it might be specific to the game you’re trying, using gamescope might help.
You can try to use gamescope for that. Really useful for games that crash alt-tabbing