You need to either setup port forwarding or setup tailscale:
To set up port forwarding on your router follow the link article. If you have two routers (for example an ISP router and another router of your choice, possibly as a part of a Mesh Wifi system then this is more complicated. If you ISP uses CG-NAT on your account port forwarding will not work.
If you have two routers in play, you should set the ISP one to bridge mode, or modem only mode, and make sure that no device other than the second router is connected to it. You may then find that simply enabling uPNP on the second router will allow everything to work.
If you can’t do this, you will need to setup manual port forwarding on both of your routers. In the ISP router, set up port forwarding to forward TCP connection on port 55002 (the ARC port shown on the Roon ARC settings page and referenced in the diagnostic text you have quoted above) to the WAN side ip address of the second router. On the second router, set a manual port forwarding rule to forward TCP connection on the port 55002 to the ip address of your Roon Server.
If you ISP uses CG-NAT, then you can ask your ISP to supply a public ip address that supports port forwarding but this may add to your monthly costs. If you don’t do this, you have no choice but to abandon port forwarding and go with a Tailscale solution (see below).
You have not given details of your Roon Server. Is it a Nucleus/Nucleus Plus? Is it a Nucleus One or Nucleus Titan? Is it a ROCK build on a NUC? Is it a PC running Windows or Linux? is it a Mac?
You have not given the requested details of your Networking Setup:
If you provide these details, I, or other members of the forum may be able to be more specific.