Used it in the past, and it’sa pretty alright desktop OS. It would work as a server OS, but that’s not really its main focus.

It’s debian based, so might as well go for actual debian.

Why? It’s a desktop distro based on Debian. Just use Debian.

Proxmox

I suppose you could, but being that it’s Debian based I’d say just use Debian.

Any particular reason?

You can

I’ve installed MX before, but I’m not sure why you would want to make a server out of it. I guess it’s possible, but it seems to me with all the hoops you’re going to have to jump through, why (not) use an OS built to be a server and be done with it?