

Yup. Install either Heroic or Lutris (though Heroic is a little better). I think there’s also a plugin to allow you to access Heroic through the Steam frintend, but in Desktop Mode, when installing a game through Heroic, it’ll add it to your Steam library, which means you can access it in Game Mode too.
You can download and keep the installers forever in your personal storage somewhere, and install them without the need of Internet connection.
When you buy a game from GOG you’re buying without DRM and have all the installers available to download as backups. Regardless of what the fine print may say, this is effectively owning your games forever.