I’m not 100% sure if this meets any of your requirements but I always enjoyed homeworld can’t remember if I’ve ever run it on Linux since switching tho.

As to the other requirements, I don’t think I found it that easy to get into as it took a while to get into the whole 3D map thing, and the graphics may have aged

I also I noticed I have

–skip-launcher

In the box for launch options in steam.

I don’t have dotnet 6 installed either and running straight from Heroic fails every time. When added thru the steam client it works.

I installed with heroic Add non steam game Highlight bg3.exe or maybe dx version can’t remember now from bin directory “not launcher” Run with proton 8.0.3 I think Crashed first time but fine since