For some days now, there is a new package in the debian repositories for Mysql. While the latest version installed was 5.7, the new one is a big jump to 8.0! Unfortunately a simple upgrade failed. It turns out one first has to run mysql_upgrade and after that do apt upgrade.

So, if you experienced some upgrade problems during an upgrade with APT, run the following first:

#Check you can connection
sudo mysql -h localhost -u <user> -p<passwd>

#If you could login, exit and run
sudo mysql_upgrade -h localhost -u <user> -p<passwd>