Hi there!
Roon ARC works perfectly on my setup: Windows 11 Roon Core and FritzBox 7590 router.
Please be aware that in many routers you need to:
1 - turn on UPnP
2 - give permission to use UPnP to automatically configure ports to your Roon core.
Without step 2 RoonARC will not work.
Cheers
Marco