After reading your helpful lines I did all steps again. Started with stopping docker containers on old-server moving config/data etc and firing up new one.
And now it is working … very strange but the effort of doing an 4h extra turn was worth it.
The only issue remaining is a error message in Nextcloud:
The “X-Content-Type-Options” HTTP header is not set to “nosniff”. This is a potential security or privacy risk, as it is recommended to adjust this setting accordingly.
The “X-Frame-Options” HTTP header is not configured as “SAMEORIGIN”. This is a potential security or privacy risk, and we recommend changing this setting.
Your web server is not set up correctly to resolve “/.well-known/webfinger”. See the documentation for more information.
Your web server is not set up correctly to resolve “/.well-known/nodeinfo”. See the documentation for more information
For caddy v2 I found no solution to solve it. All efforts are already in my Caddyfile?!
Thanks