After Upgrade to Ubuntu 20.04: "Oh no! Something went wrong"

This will go a long way toward making that "Oh no something went wrong!" sign go away. First, press Ctrl+Alt+F3 to trigger the CLI, and login. Execute the command:

sudo apt-get update && sudo apt-get dist-upgrade 

to continue upgrading. Your machine will install the missing resources, and finish upgrading, and then you just have to clean up and reboot:

sudo apt-get clean && sudo apt-get autoremove && sudo reboot

Best of luck!

My question has been answered cooperating with Ollie:

• sudo apt-get update resulted in "Could not get lock /var/lib/apt/lists/lock. It is held by process 22027 (focal)"
• I tried to identify the process with ps aux | grep -i apt and ps -aux | grep -iE "apt-get" which didn't work, but I could identify it with pgrep focal which gave me its process ID. I killed it with sudo kill <process_id>.
• do-release-upgrade worked for me only without the -y option. It resulted in "There is no development version of an LTS available. To upgrade to the latest non-LTS development release set Prompt=normal in /etc/update-manager/release-upgrades"
• Then I ran sudo apt-get upgrade -y and got the message "0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded". The 1 not upgraded was an expired libc++1 package.

Rebooting the computer, Ubuntu 20.04 worked well.

(I then installed the current version of this libc++1 package via Synaptic.)