All (most?) Steam games have a very simple DRM that is extremely easy to bypass, and you can find examples on github.
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 see, but there is Steam DRM there. So, I guess as the other commenter was alluding to, if Steam goes belly up so does your collection, regardless of the dev studio's intention (Or atleast, locked behind a DRM bypass).
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)
I tried to search if it's possible for a dev studio to release a game on Steam that works without it, by which I mean that if I uninstall Steam, the games keep working; I wasn't able to confirm, but it seems to be theoretically possible...
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.
Definitely not all games, and for games that do have it cracking it is in most cases as simple as swapping out a Steam .dll (so very easy). It's primarily there as appeasement for devs who would be reluctant to engage with a platform with no copy protection, or in otherwords is mostly theater.
I haven't tried with too many games since the usecase only comes up rarely, but I know that Downwell and UFO 50 work this way off the top of my head. They come with a Steam dll that will try to launch Steam for the sake of getting achievements and such, but if you delete them or just don't have Steam they launch all the same.
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.