H again,
I solved my problem of backup using Docker container NCP:
By restoring the persistent volume to exactly the same folder, the new container works perfectly well.
The problem was that my backup persistent volume had a different path AND the database needs the paths to be the same.
I did not find a way to migrate NCP installation to run a new docker container with the data backed up in a persistent volume with different path.
if anyone knows how to do such migration, I would like to try it out.
thanks for the previous replies pointing me in the right direction.