SOLUTION 1
Purge out (or remove if you want to keep databases) any mysql packages to repeat the installation anew:
sudo apt purge "mysql*"
-Autoremove packages
sudo apt autoremove
-Stop the apparmor service
sudo systemctl stop apparmor
-Make apparmor drop its profiles (I thought with stop it was enough, but for me it wasn't. With systemctl it doesn't work)
sudo service apparmor teardown
-Reinstall mysql-server
sudo apt install mysql-server
-Install apparmor-utils, to create a profile for mysql in apparmor that allows mysql to run
sudo apt install apparmor-utils
-Check the status of mysql-server (must be Active(running))
sudo systemctl status mysql
-Generate a profile for mysql in apparmor
sudo aa-genprof mysql
-In other terminal run mysql (enter root password)
mysql -u root -p
-do things in MySQL while apparmor is generating the profile in the other terminal
mysql> CREATE DATABASE fooDB
-Swith to the other terminal and press "s" (the prompt tells you it's for "scan")
-Say yes to the policies from apparmor you see fit (I guess all of them for mysql), say yes pressing "a" for Allow
-Press "f" to Finish the apparmor profile
-Restart the apparmor service
sudo systemctl start apparmor
-Check to see if you still can use mysql in the other terminal
mysql>exit
mysql -u root -p
If all is well you can use mysql from the command line.