Not an epic journey.
Switched back to Gnome Shell from Ubuntu MATE desktop after 6 months, mostly because it was becoming as difficult to do nonstandard things in MATE as it had in Gnome. Although I tried simply re-installing Gnome and switching to it, all the cruft that had accumulated, including an in-place upgrade from Ubuntu 18.04 to 20.04 LTS, eventually got the better of me. Three hours in I was stuck at the Plymouth splash on both my desktop and laptop. On to Nuke and Pave.
Well, not exactly. All I did was do a minimal install of Ubuntu 20.04 LTS Desktop to my root (/) partition and left /home and the data volumes alone. It took a while (around 2 hours working on two machines in parallel), but I got it done.
This time around I had to create an EFI partition out of my existing root volume because that's how Ubuntu rolls now. That was easy enough: the "something else" option in the installer lets you blow away a partition and then create whatever you need in the unused space. I went with a 512M EFI partition at the beginning of the disk, and filled out the rest of the space with an ext4 formatted root. I left my small (4G) swap in place on the desktop, but let the installer bludgeon me into using a swapfile on the laptop (honestly, I was too tired at that point to figure out why it was fighting me on that).
After the install I had a bunch of customizations to do, starting with installing any software that wasn't already setup in my home directory (I run pyenv, nvm and a bunch of other programs -- including AppImages -- in $HOME). My "List of useful software", covered most of what I needed. I also referred to "Add a bridge interface to Ubuntu desktop using nmcli", "Setting up a bridged network for KVM guests", and "Ubuntu Server Setup - with netplan" (on installing chrony and fixing resolv.conf). Of course I had backups of the previous configuration to refer to while I worked, which helped when it came to things like what /etc/sysctl.conf needed to look like.
