As @Maarten_Duits points out, the port forwarding diagnostics you’ve provided suggest that UPnP is not properly configured on your router or not working correctly.
Please try the following steps in order:
Reboot your Roon Core and networking gear (router, modem, switches, etc.)
Try to enable UPnP/NATPMP in the web administration interface for the router
Try to manually open the port in your router’s port forwarding configuration
Make sure the IP/Port matches the Port listed in Roon → Settings → ARC
Check for any VPNs or Firewalls that might be interfering
Try to update your router firmware
Check if your modem is in Bridge mode and if not, try to place into Bridge mode
If you continue to experience difficulties, please tag the support team and include the following information:
What is the make and model of your modem and router?
Do you have any additional network hardware, like additional routers or managed switches?
Who is your internet service provider and what is your geographic region?
Is your Modem configured in Bridge Mode so that it operates only as a modem or do you have the ports forwarded on both?
Just checking in, as diagnostics suggest you might still be having an issue setting up port forwarding.
To echo the helpful suggestions from the Roon Community moderators above, please try enabling UPnP in your router web administration first. I also recommend installing the most recent version of Roon and ARC on your devices, as we’ve been making incremental improvements to sync and connectivity since you originally reported your issue.