I don’t think popular games will ever be fully open source, but our operating systems could be.
I have very little proprietary software on my system outside of games, and it’s mostly limited to a handful of firmware blobs (e.g. GPU and WiFi firmware, CPU microcode, etc), with the clear exception bring browser DRM for streaming services. Everything proprietary on my system is sandboxed in some way, so I’m reasonably protected from most of that nonsense, but it’s still there and probably always will be.
Having proprietary software isn’t the issue IMO, as long as I can sandbox it. I can’t sandbox kernel level anti-cheat, so I’m never going to install a game that requires it. That’s my line in the sand.