Syncthing for Docker is not a final solution for my case for various reasons.
When I synchronize files, they are created twice, in the container and in the data directory on the server. If this “double occupancy” can be avoided, I would be happy to learn more.
I find the administrative effort of storing all possible directories in the Docker configuration high. This is justifiable for a few directories, but not for around 60, as in my case.