I've found that some old PC titles are available on Steam, DRM free (if you're willing to futz with the install directory -- they're running open source game engines and proprietary vintage assets; you can just copy the assets out).
Typing this reminds me: I should look into switching to GOG for such purchases.
And even if they’re not, a lot of games (used to) use Steam’s DRM and then never actually called the extended license check APIs. That’s to say that a lot of times the same “steam_api.dll” that pirated games have may work for a bunch of games.
I found that out a few years ago when I tested out virtualization graphics performance and wanted to avoid installing full Steam every time for my (legally purchased) games.
Typing this reminds me: I should look into switching to GOG for such purchases.