Sort of solved.
The core of the problem was, as I noticed above, that MariaDB now gives back the client version, not the server version, so the Connect fails. Using SkipLibraryVersionCheck bypasses this problem. It would be good to fix it though.
Then it still did not work, but that is an old problem, that a variable in the testing program was named SQLConnection and this is also the name of a property in tSQLTransaction so in a with statement it picked up the property not the variable. This I had once in the past, this is why I start the variables sometimes with My..., but now I forgot it in the test program and thought that it is still related to the original MariaDB problem. So, thanks for looking into it, but this part was my fault.
And a third thing. I saw on gitlab that now there is support for 8.0 as well. I copied the mysql80conn and mysql80dyn files and the relevant updated .inc files, but I cannot add them to the uses. What else is needed to be changed?
Thanks,