Have you seen protondb? A pretty impressive number of games just work. Really we are at the point now where games that don’t run are more the exception, and usually it is due to Anti-cheat incompatibility or some very specific issue.

ALVR works great, assuming SteamVR in general works with your DE (no Gnome support atm but KDE works for sure).

That display out will be hard to match with an old optiplex or laptop, but I agree, the pricing is getting less absurdly low and more just moderately low.