It looks from the diagnostics that upnp is not active. You can also see that your actual external ip address is found but not the internal one. I had this problem when I deactivated upnp and didn’t have the port forwarded manually.
Bear in mind that you might solve this internally only to find that your ISP uses CGNAT and you won’t be able to connect anyway, but in the meantime make sure you have upnp activated and maybe reboot the router and wait for it to connect before trying again.
It is quite complicated to understand in the beginning. If you are based in an english speaking country there may be other terms but I would search something like CGNAT community fibre, where community fibre is the name of my Internet Service Provider or ISP. It is very likely that you would find someone talking about that supplier and CGNAT if they use it. CGNAT stands for Carrier Grade NAT, you might have more success searching for that.
Essentially it’s a way of sharing addresses on the internet which ISP’s have adopted to save money (and addresses which are numerically limited).
If you can establish whether your ISP is using CGNAT you can save yourself looking for any other problems in your setup.
As Andy has said above, it looks in the error message that the UPnP on the router is not enabled. You would have to enable this (and as Bob wrote, this can be done per device in the Fritzbox) or configure port forwarding manually on the router:
It may or may not work after this. If not, there will be a new error on the ARC tab in the Roon Remote. Post this one, too. It’s possible that you may have to call Telekom and ask them to enable an IPv4 address for you that is suitable for port forwarding. But let’s try and see
It’s fine for me, I am Austrian and living in Berlin But the screenshot you posted is not it. This Fritzbox help page explains how to enable port forwarding (Portfreigaben in German) automatically with UPnP or manually by entering the port number (which you get in the ARC tab in the Roon Remote):
After this, the ARC tab in the Remote may show that it is working, or it may show another, different error. If there is an error, copy and paste the error message again