The number of games like this (that work without Steam) is vanishingly small ime, and there is no way to tell in advance whether a game will work or not. (I have actually had a lot more success with the Epic Games Store.)
Altough incomplete, PCGamingWiki has info on whether games work without steam DRM. AFAIK they are usually tested by moving the game folder and running without opening Steam.
Not saying that there's a lot of games where the publisher/dev made this choice, just responding to OP saying its not possible with steam. Unfortunately the store doesn't show drm free games either.
I am aware that there are some games that you can download and happen to be able to play offline if the steam launcher executable simply happens to be a dumb link to the 'true' executable which checks for a steam connection first, and you could in theory find out where the 'true' executable lies in the game folder, because of the way it's designed. But I would hesitate to call this a "DRM-free" game in that sense; more like "the DRM is trivial and easily bypassed if you know what to run".
Furthermore, there is no guarantee that just because it works "DRM-free" now, it will continue to do so later. Or, just because it "works", it doesn't mean that somewhere half-way into the game there isn't a "check" or "achievement" that won't crash your game.
etc.
And in any case, Steam does not have a commitment towards DRM-free, not even in the sense of at least committing to flag such games as such. It's all 'accidental' at best. And while it's the last games company that you'd expect to go bankrupt 'now', all your games are in theory 'licensed' content, not 'owned' purchases. It's entirely up to them to remove content without notice (because you bought a game in one country and then moved to another, e.g.), or go bankrupt and say well sorry, some games might work if you download them but we don't guarantee anything.
Whereas in theory, GoG will let you make a full local backup of your entire collection, and in the few games that (annoyingly) "subtly" break the DRM-free promise (typically due to the way multiplayer is handled), these are clearly signposted in the store pages.
After you do what I said you can copy the directory and run it anywhere without steam or internet connection. You said its impossible, like steam forces it this way, but it clearly doesn't even if only very few Devs make this choice.
https://www.pcgamingwiki.com/wiki/The_big_list_of_DRM-free_g...
e.g. https://www.pcgamingwiki.com/wiki/Hades