They do work without steam. Steam has just streamlined the process.
And of course you'd need a compatibility layer (e.g. wine/proton). But those aren't dependant on Valve. Even though they've definetly benefited from their involvement.
Protondb also has some hard numbers. There are some 12000 games that are playable on the steam deck. Also something like 70%+ of the top 1000 steam games are platinum or gold rated which means they work out of the box with zero or minimal effort.
They do work without steam. Steam has just streamlined the process.
And of course you'd need a compatibility layer (e.g. wine/proton). But those aren't dependant on Valve. Even though they've definetly benefited from their involvement.
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You can check community reports on http://protondb.com
It's an estimation since proton has made such giant leaps. When a new game releases, you can assume that it runs on linux.
Protondb also has some hard numbers. There are some 12000 games that are playable on the steam deck. Also something like 70%+ of the top 1000 steam games are platinum or gold rated which means they work out of the box with zero or minimal effort.