Ubuntu Server ​

Focusing on a server, the requirements are a bit different. It doesn't matter if the server is physical or virtual. Ubuntu even makes a server distribution tailored to Raspberry Pi's, so this is a good place to start for those.

After installing Ubuntu Server, log in to the machine's console.

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SSHD ​

Best to enable SSH service so you can connect remotely. This is a nice, up-to-date write up of the different considerations for ssh configuration.

https://help.ubuntu.com/community/SSH/OpenSSH/Configuring

sudo apt-get install openssh-server

Then, SSH access should be on and available remotely

It might be a better idea to use SSH Keys and disable password authentication, especially on a publicly visible server

sudo vi /etc/ssh/sshd_config

From here, it probably makes sense to use configuration management. Documentation is okay too!

Desktop ​

If you want a desktop GUI, you can add one:

sudo apt-get install ubuntu-desktop

(This worked for me with a Raspberry Pi 4 with 4GB of memory and Ubuntu Server 20.04)