6. Seriously, why not Ubuntu Focal on Raspberry Pi 4 ? - HaroldSP/Harold GitHub Wiki
Ubuntu Focal
The general installation process is shown on that video. Here are some useful commands and tips to navigate in your new system:
Get the information about your GPU memory:
grep -i --color memory /var/log/Xorg.0.log
Output:
[ 40.249] (II) FBDEV(0): hardware: simple (video memory: 8100kB)