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Prerequisites:

VM-Creation

I have already uploaded the necessary ISO to a folder to a datastore.

OS - Installation

References:

Get Ubuntu Server | Download | Ubuntu
Get Ubuntu Server one of three ways; by using Multipass on your desktop, using MAAS to provision machines in your data centre or installing it directly on a server.
Ubuntu

https://it-infrastructure.solutions/how-to-set-up-ubuntu-20-04-1-desktop-amd64-in-a-virtualbox/