WebRTC call between two networks connected to the same server

I currently have the following network setup and would like to be able to make WebRTC calls between the two clients in different networks.

I enabled IPv4 forwarding on the openSuse Leap 15.2 server and both devices have either 192.168.2.1 or 192.168.4.1 as their default gateway. The web application as well as the signaling service are both hosted on this server as well.

With the Firewall disabled the call works as suspected, but with the Firewall on the call no longer works. I thought about hosting a Coturn STUN/TURN server on this server, as I've read that you should provision one, if you run into troubles with a firewall.

Is a setup like this doable with lets say Coturn and what would the configuration look like for a scenario like this?

I ended up solving it as I describe in my GitHub issue for this matter.