@rpgfreaky I've spent all day yesterday and today trying to fix this issue using most of the provided solutions online (most if not all youtube videos about the issue, microsoft forums, microsoft's two support pages for this issue). I restarted and tried to reconnect Teredo through CMD in all ways possible, reinstalled the Teredo Tunnel Adapter, at last deleted my Antivirus and VPN programs and drivers with a heavy heart like it was suggested on the official microsoft page, also restarted over and over, opened Forza-/Teredo-specific ports on my router and system, changed DNS, changed servernames and types for the Teredo connection etc..
And yes it's one big complication that for some reason Microsoft felt the need to remove the repair-button for the Xbox Network Tab which also is entirely gone now under windows 11 settings and has been moved to the "Xbox companion app". Sadly there you wont find a repair button either.
Perhaps they thought its the same as going to the list of apps under windows settings and repair and reset the Xbox apps on their app page? For me, nothing worked. Sadly there isnt even a replacement for this removed xbox-network-quickfix under "troubleshoot".
The issue could be Windows 11, i have to believe. Perhaps we all need to wait for the official release...? I really doubt that this insider preview is prohibiting the teredo service from connecting, but I ran out of options on what else to believe in..
Anyway this is what it shows to me now (with added comments "//"):
// I translated some of it from German to English.
Type : enterpriseclient
//has also been 'client', 'natwareclient'.. currently switches a lot to 'disabled' and under state shows 'offline' and then changes to whatever client i changed it to via cmd after a while;
Servername : win1910.ipv6.microsoft.com.
//has also been "teredo remlab" "teredo fix fi" or whatever they called in on youtube;
Client refresh interval : 20 seconds
Clientport : 3544 (Group Policy)
//i changed that from "unspecified" to this, through group policy, which was also suggested online;
State : probe (primary server)
//no idea what that means, probably not good since it should say "qualified";
Clienttype : Teredo host-specific relay
Network : managed
//said "unmanaged" all the time until now, but still wont connect;
So yea there are lots of parameters you can freely change there via cmd etc. to see if it works, but I am more than confident that once windows 11 releases, posts about this problem will spread and there should be a fix or a solution underway sometime soon.
Also i was thinking whether i should just get Forza 4 on steam but I'm guessing it uses the same teredo service, even though online the portforward site shows different ports for steam (no idea if its that relevant).
However, Xbox game pass games like Tetris Connect actually DO work through the xbox app, but perhaps because it doesnt use the teredo service...
Hope my post was of any help for you, Im rooting for a fix here as well.
