StarShocked

I use Flapak to run Beyond All Reason. It does include its own updater, which makes it more portable.

I'd recommend Beyond All Reason. It's open-source and utilizes a realistic scifi theme. You essentially manage metal and energy to produce more units, to fight against other player's units. It's very easy to learn, and looks nice graphically. The only caveat I can think of is that it is not on Steam. Game Link: https://www.beyondallreason.info/