If you’re setting up Proxmox either use the Proxmox ISO or start with Debian Bookworm. The only Linux machines I have with a GUI are my desktop and my laptop, both running Debian with KDE. All my servers run Debian unless there’s a good reason not to.

I found myself in a similar situation last year. MXRoute’s lifetime plan works well for those domains that just need basic email and not a lot of storage.