@mitu
thanks a lot for that hint! I've checked the issues, but didn't notice this one.
For anyone interested/impatient, appending the following works for now:
videodriver kmsdrm
to
/opt/retropie/configs/mame/mame.ini
Just remember to remove it when it has been implemented, as mentioned in the pull request above.
There don't seem to be any other references to fbturbo or Allwinner in the remaining configuration.
Then I don't understand from where the fbturbo configuration is referenced.
Can you check if the file still exists after you remove the xserver-xorg-video-fbturb package ? If so, remove it and see if - after rebooting - you still get the error.