Here to the rescue!
Do this first:
https://techcommunity.microsoft.com/t5/windows-insider-program/teredo-problem-on-windows-11/m-p/2614126
Then: if you still have issues:
https://www.minitool.com/news/microsoft-teredo-tunneling-adapter.html
(The second DOES include a registry edit, I did everything I could to avoid having to do it, but ended up with that anyway. So long as you take your time and follow the instructions: it isn't too bad for anxiety.