

It depends on the project/container. Some containers run Debian, some Alpine, some Ubuntu. I mostly rely on the community scripts from here and use the defaults.
https://community-scripts.github.io/ProxmoxVE/
I guess everything that supports containers, QEMU and KVM is compatible to use as a guest OS in Proxmox.

I really liked the Custom Maps in Warcraft 3 online play. I used to play Hero Line Wars, Mauls and TDs, Dota, Legion TD among other amazing community made maps