As I’ve been through this, I may be able to help @Akimo. Though I’m not the last word expert. All the ports in the port-forwading schema are 55000 for the first pass.
- “Listening port” in your Roon application / Roon ARC/Mobile setting
- Internal and External ports in your router’s settings
Hope this helps, and/or I’m abridged with better info by our more esteemed/knowledgeable tester colleagues. The above is what worked for me as I sequenced through my initial port-forwarding issues when I came on board a few weeks ago.
HERE is a long thread, showing the step by step with screen snips to my problem and solution components.