Solved it.
2 years ago I have implemented Multi WAN Setup and introduced a Group Gateway.
https://docs.opnsense.org/manual/how-tos/multiwan.html
The new VPN Gateway was automatically included in the Gateway Group but with action to never be chosen. Therefore no traffic could enter the Gateway and the tunnel.
After disabling the group it works like explained in the docs.
2 years ago I have implemented Multi WAN Setup and introduced a Group Gateway.
https://docs.opnsense.org/manual/how-tos/multiwan.html
The new VPN Gateway was automatically included in the Gateway Group but with action to never be chosen. Therefore no traffic could enter the Gateway and the tunnel.
After disabling the group it works like explained in the docs.