Just in case someone else has the same problem.
It seems that i have a workaround.
After Init Done with the failed startup of MariaDB message do following:
stop the containter
sudo docker stop nextcloudpi
And remove it:
sudo docker rm nextcloudpi
Change the nc-limits.sh script in the data-directory under bin/ncp/CONFIG by replacing the line under DATABASE MEMORY
AUTOMEM=$(( TOTAL_MEM * 40 / 100 ))
with
AUTOMEM=$(( TOTAL_MEM * 20 / 100 ))
Then Recreate the container (with the same data-directory without deleting the content!)
docker run -d -p 4443:4443 -p 443:443 -p 80:80 -v {data-directory}:/data --name nextcloudpi ownyourbits/nextcloudpi-armhf ${DOMAIN}
I think limits.sh does not work for 32-Bit OS with 8GB memory cause it tries to allocate more than 3GB of memory which is not possible and leads to the MariaDB failing on startup.
For 64-Bit OS there should be no problem.
If there is a better solution please report