Ubuntu is primarily Ubuntu-based for example.

I’m up for Gnome, Xface, Cinnamon, KDE or whatever DE.

…on a headless server. What does the word "headless" mean to you?

I'm familiar with Ubuntu based systems

Then use what you're familiar with. Done.

I think many here misunderstood your intention. The combination of "server" and "what DE?" is a weird thing for most of us, especially since you said headless, which usually means no desktop, only ssh and stuff.

But I think I understand what you are up to.
You want something mainly for gaming, where the PC acts as "brain" of the games, and you only stream them to a low-power device, similar to what Stadia was planned. Right?

For that, I'll recommend Bazzite with Moonlight or how it's called.
Bazzite is a gaming oriented Fedora Atomic spin that has Nvidia-drivers already baked in, updates itself (you only need to reboot once in a while) and gives you a great experience, even offering to boot straight into Steam's BPM.

Moonlight/ Sunshine/ whatever is a screen sharing protocol or software that allows you to stream games without latency or much quality loss.

I'm no pro tho, so take my suggestions with a grain of salt :)

You can use Ubuntu, but I'd highly recommend Debian. You can expect all the package management stuff you know would work, since it also uses apt.

I would use Bazzite 100%. It's an atomic fedora spin that aims to replicate SteamOS. It has a KDE Nvida variant, and comes preinstalled with all of the gaming software and optimizations you need out of the box. All that is required to update it is a restart.

Just switch to X11 from Wayland after first boot and you're as good as gold. (If Wayland works fine with your card it may be a better option because I think it plays more nicely with BigPicture mode if you need that)

VNC is a security hole unless you route it through an SSH tunnel. If you're managing a docker container for jellyfin there's not much UI work to be done anyway.

If you familiar with Ubuntu and its derivatives, just use Ubuntu.

Ubuntu provides a server version called Ubuntu Server alongside the desktop versions if needed, and Ubuntu provides easy access to things like ZFS.

You can always switch in the future if you find you have server needs or preferences the Ubuntu doesn't suit.

Maybe Vfio powered virtual desktop? You could install Proxmox and then pass though the GPU to a VM.

For remote access you could use Sunshine/moonlight

For Jellyfin I would create a different VM running Debian with your integrated graphics passed though.

Ubuntu Server seems the obvious choice. Just roll with the DE it will install as dependency for one of your needed apps.

I would recommend ublue bazzite or secureblue (nvidia userns kinoite). Never used VNC on wayland as clients that dont need static IPs suck or have no wayland support. KDE has software for that.

Bazzite would be the easy solution as it is a very well curated image (with lots of variants) for gaming.

Secureblue is not for gaming, so you will need Flatpak for Steam, Bottles, Lutris and PupGui or whatever you use. Or you layer everything, which will slow down updates but as a server its not that bad. But secureblue is a "proof of concept" of a secure Fedora. You might encounter new bugs as its currently not meant for gaming, and this will be helpful to improve radical security trends for Fedora (secureblue does lots of things Fedora doesnt, as it is a clear secure distro, not "it works kinda and always").

Ublue (and all derivates like bazzite or secureblue) has the drivers preinstalled and if the addition breaks something you will likely just not get an update, rather than have a broken local system.

Please report your findings!

After doing some research I'm surprised that nobody here mentioned Nobara. I think it fits neatly here.