I think you'll probably be fine with Stellaris. Though I'd be curious to know how your benchmarking goes. You may even want to consider trying a few different distros. I don't care much for Pop OS but I thought it was supposed to be optimized for gaming. Manjaro has pretty decent out-of-the-box driver configs too, though that distro has its own issues separate to gaming. If you're on Ubuntu you may have to manually point the system to proprietary drivers too.

I've seen some other weirdness with Proton emulation, but ProtonDB is extremely helpful at troubleshooting.