I have performed an upgrade according to the following instructions.
https://support.plesk.com/hc/en-us/articles/213403429-How-to-upgrade-MySQL-5-5-to-5-6-5-7-or-MariaDB-5-5-to-10-0-10-1-10-2-on-Linux-?page=6
In principle the upgrade worked
At the end there are two commands:
# plesk bin...