I installed the latest 18.04 updates with Software Updater and hit upgrade (to go to 20.04 from 18.04) and nothing happened. According to Synaptic, I have no broken packages.
I would like to stick with the GUI upgrade process rather than the command line.
I don't know if this is related, but I recently uninstalled openssl1.0.2 because 1.1.1 was also installed and the 1.0.2 headers were preventing me from compiling Python3.10. This apparently broke the calculator and system monitor apps - which is the main reason I'm trying to upgrade.