Hi
It is a long time since I looked at this so I need to do some research again!!
I see you now have MySql 5.7.39 which is certainly above the minimum requirement.
jD does a check at the early stage of the upgrade and I see that the relevant part of the report is " but your current database MySQLi is version 5.5.62-38.14-log and is not supported".
It would appear that either jD is picking up the wrong information or the relevant location is not itself correct

I will set up a test site to do the upgrade to check where jD finds the info about the MySql version.
In the mean time could you please go to System - System Information and check which database version is shown
Colin