NAT was a hot topic throughout the Xbox 360 era, and it still plays a sizeable role for Xbox One and Xbox Series X|S. Manually assign an IP address to your Xbox One, using the previously fetched IP and MAC addresses. Step 1 - Assigned a Static IP Address to your Console. Open the Airport Utility app, choose your airport device to be configured. Not everyone is going to have that as an option.AT&T still gives people a Netgear(aka Westell) 7550 Gateway that doesn't even have UPnP at all.The port forwarding and port triggering is disabled on it as well without any explanations from AT&T.Even most newer routers that are made can't handle more than 1 Xbox without NAT issues.Some of the extra ports are for testing to make sure that there isn't a connection error. It's also not 100% clear from what your issue is, but seems that you can't connect to xbox live over Teredo tunnel.
Some basic things to check are trying a different port on the gateway and a different network cable. Another way to fix this is to hardwire the router and the xbox in. I would not recommend using 3rd party firmware if you have no idea what you are doing as this can cause the router to become a brick.
Make sure you have Xbox One App Installed on your Windows 10 PC. If your Xbox console has IPv6 connectivity, your Current Network Status will read IPv4 & IPv6. If it demonstrates the result as error: none, then all the Teredo is Unable to Qualify Xbox App.
