this happened to me too
the solution is to remove mysql completly from the server ubuntu 20.04
*Note: not recommended if you already have databases. this work only if you have fresh aapanel installed.
remove MySQL server:
sudo apt-get remove --purge mysql*
remove the purge:
sudo apt-get purge mysql*
uninstall mysql completely without leaving residue files:
sudo apt-get autoremove
after you finish try to reinstall mysql from aapanel.
