I only boot windows for Fortnite and The Crew 2 because of BS DRM. Everything else runs great.

Yes. I switched to PopOS a few months ago from Arch seeking a "just works" OS for gaming. It's been great for me.

Sorry for the late reply. You can replace the optical drive with a 2.5" HDD or add a sata PCI-E card since your not using the GPU slot in this case. My personal setup uses an NVME for the OS (DietPi), and two 6TB external HDDs on an Optiplex 5060 SFF.

I'd buy a Dell Optiplex 5060 for about $200 off eBay and you'll get an i7-8700 with a 630 iGPU and the NVME taken care of. Then you just need the hard drives and more RAM. My home server is just fine with 16GB of RAM, though. There's no DE and I don't game on it.

Yeah, direct play only. Nothing over 1080p.

I use an Odroid N2+ running DietPi (Debian) for my home server. My kids and their cousins play a Minecraft world together and I haven't heard any complaints. It's my plex server and a web site, too. https://www.makeuseof.com/odroid-n2-raspberry-pi-4-compared/