Yes, the public IP is correctly detected.
I've also reverted the custom.conf of unbound except the entries pointing two the two other applications in the network.
However, it's take around 10 min to install an application because it still runs into the acme challenge timeout, but in the end most of the apps seem to work properly.
And the following picture does not help for receiving certificate:

So I guess, after timeout it the falls back to the domain certificate, but in the end the certificate that is in use comes from nginx on raspberry.
You can check on RocketChat application on chat.<domain.org> whereby the <domain.org> was sent to the support mail box.
But for application like OpenVPN it still not working properly. The application is online vpn.<domain.org>, but there is still the socket.io error within the log and therefore it cannot establish a connection to the VPN server.
Feb 14 10:12:12 GET /socket.io/?EIO=3&transport=polling&t=NxtWFkM 404 1.803 ms - 149
Feb 14 10:12:14 GET /socket.io/?EIO=3&transport=polling&t=NxtWGE5 404 1.512 ms - 149
Feb 14 10:12:20 GET /socket.io/?EIO=3&transport=polling&t=NxtWHiM 404 1.962 ms - 149
Feb 14 10:15:44 GET /socket.io/?EIO=3&transport=polling&t=NxtX3NF 404 1.124 ms - 149
Feb 14 10:15:50 GET /socket.io/?EIO=3&transport=polling&t=NxtX4s6 404 0.455 ms - 149
Feb 14 10:15:50 GET / 200 5.134 ms - 962
Feb 14 10:15:50 GET /js/index.563345b1.js 200 1.901 ms - -
Feb 14 10:15:50 GET /js/chunk-vendors.e7987ea7.js 200 4.398 ms - -
Feb 14 10:15:50 GET /api/profile 401 0.665 ms - 2
Feb 14 10:15:51 GET /logo.png 200 2.891 ms - 30393
Feb 14 10:15:52 GET /socket.io/?EIO=3&transport=polling&t=NxtX5Ln 404 1.404 ms - 149
Feb 14 10:15:58 GET /socket.io/?EIO=3&transport=polling&t=NxtX6py 404 3.699 ms - 149
Feb 14 10:16:00 GET /socket.io/?EIO=3&transport=polling&t=NxtX7Jb 404 0.470 ms - 149
Feb 14 10:16:06 GET /socket.io/?EIO=3&transport=polling&t=NxtX8nN 404 1.397 ms - 149
Configuring like this prevents the socket.io error from being written into the log, So I guess this is progress...

But still the OpenVPN is not able to establish connection: Connection Refused.
And this did not help to resolve the issue:
