First of all, thanks for doing this. I really appreciate it, game preservation depends on DRM-Free packages. And there is no other software that I know of that is trying to offer the closest thing to a Steam-like experience for this scenario.
With that out of the way, I must bring up a specific section found in your documentation.
It simplifies the whole gaming experience by organizing, downloading, installing, playing, and tracking
https://gamevau.lt/docs/client-docs/how-to-use
From what I can read in the docs, the installation is completely manual. Even games that don't have an installer, they get compressed and must be manually decompressed to the proper gamevault folder.
If games that don't require an installer, actually do get automatically "installed", then my suggestion is that you add that to the documentation. If that is not the case, then I suggest you stop advertising this functionality as if it was true.
As for Linux, if this software does offer an advatage over just copying games, I guess someone will eventually make a plugin for Lutris or Heroic. But one thing that I suggest for GameVault is developing a way to automatically add the games as a non-Steam game to the Steam application. The majority of users prefer Steam over any other launcher, specially for people using their PCs connected to a TV, Steam Big Picture is just superior to anything else out there.