You're not doing anything illegal at the moment you do it
You can use it to play the game on a different computer (as long as the game is DRM free which is not granted on either platform)
The company (Valve/GOG) can't remotely erase your copy
If the company removes the license from you your backup is now technically illegal but it's unlikely to be enforced

I fail to see how GOGs approach is any different, they still sell you a license and you're backing up the installer in case the license gets removed and/or you're forbidden from redownloading the game.

[–] lepinkainen@lemmy.world 2 points 14 hours ago (1 children)

So you can just pop that folder on any computer and run it, without installing Steam and without a Steam account?

[–] Nibodhika@lemmy.world 1 points 14 hours ago (1 children)

On most games yes, like I said before I've copied games from my computer to others to play in lan to convince friends to buy a game.

Then there are badly implemented games, where you need to either delete the steam library from the game folder or replace it with an open implementation.

And the rest are the ones that have DRM (which are not available on GOG anyways so they don't matter for this discussion).

[–] RmDebArc_5@sh.itjust.works 2 points 7 hours ago (1 children)

Actually, some games have DRM on steam and have a DRM free version on GOG. I even saw a game that had a DRM free epic and gog edition but the steam version had DRM. Might be a edge case, but still exists

[–] Nibodhika@lemmy.world 1 points 6 hours ago

Yes, there are a couple of corner cases, I know of 1. But what I stated is still true as a general rule.