Can't you just add physical PC games to your Steam library rather than having to buy them twice though? I know I've got the physical disc for a bunch of PC games that I've added to my Steam library and can now just download from Steam whenever I want without having to use the disc. It unfortunately doesn't work for games not on Steam though.
If the game uses Steam from the disc version, I'm talking about games from the 80s, 90s, early 2000s, etc. that were pre-Steam or that didn't come with a Steam version.