Akonadi not working after Upgrade from Ubuntu 19.10 to 20.04

After the upgrade the Akonadi server did not start. The respective error messages when starting it manually again pointed to a database problem. The reason was that the maria db server was not allowed to access my personal files thanks to AppArmor. To fix it, I had to apply the following partch to /etc/apparmor.d/usr.sbin.mysqld:

  /run/user/7503/akonadi/* rw,
  /home/wilmes/.local/share/akonadi/** rwk,

This is very specific to my personal user, so it would be better to replace my user name by some wildcard but I just do not have the time to look deeper into this. This must be sufficient as reminder for the next time this happens ...