However, a lot of games add their own DRM and/or protection scheme that complicates things.
EDIT: technically there are two distinct component: the actual DRM, called steamstub, and the steamwork library, that does not work without steam but it is not considered drm. Both can be easily bypassed/emulated.
I understood this in terms of Live Service games, but did not consider Steam's ability to shut down their own platform and kill my locally installed single player games with it (Again, I'm seeing its possible and seems easy to bypass usually, but the principle of the matter)
None of the games I have in my library work like that, but online some people suggest that some games work even without Steam, once installed.
Your point, however, still stands.
I would like to test it for myself to confirm it.
Google turns up this Steam curator that lists games that run without Steam and are DRM-free out of the box, though it seems far from comprehensive: https://store.steampowered.com/curator/38523697-DRM-FREE-GAM...
The PC Gaming Wiki has a couple of better lists it looks like: https://www.pcgamingwiki.com/wiki/The_big_list_of_DRM-free_g... and https://www.pcgamingwiki.com/wiki/List_of_DRM-free_games_on_...