I run a fairly standard arch setup and have had very few issues with games. I've done a bit of tinkering with bottles, lutris, etc, but pretty much everything just works first time with steam.

I've only had to set a few launch flags, usually for a game to use directx instead of vulkan or vice-versa. Sometimes you can't play a game on launch, but usually one of the first few patches will get things in working order. Steam deck popularity has done wonders for this aspect.

The most common issue I run into is a game update that will break or degrade the experience. But usually those get fixed fairly quickly in follow up patches. A lot of developers will skip testing in proton (mostly because itll "just work" these days) but i imagine theyll start doing so more often before pushing updates as steam decks and Linux become larger shares of players.