Teredo General Fix 0.6.1, Updated 02/03/2023.
If you think i skipped some informations or you found an other solution not included here, you can create an issue or a pull request here on github and i'll try to implement it inside the teredoFix.bat, the ultimate goal is to create a general fix for every teredo/openNAT-related problem in the xbox app / microsoft multiplayer.

📖 INSTRUCTIONS

Remove any VPN software, disable firewall protection in thirdparty antiviruses, keep windows firewall enabled and on standard settings (check extras if you want to reset your windows firewall).
On this github page, on the top right, press the green button "Code" and than "Download zip" to download the fix script, unzip the folder.
Run teredoFix.bat, windows defender will show up, click on More informations and then Run (code is open-source so you can check that it is safe), computer will automatically reboot in 30 seconds. Fix is done!
Check if you have open NAT (You can check only on Windows 10) go to: settings > games > xbox networking, if you still don't have open NAT try to use the "Fix" button in windows settings and than reboot or else you may have to access your router and set a port forward that redirects incomming traffic to your public ip address on port 3074 to the local ip address of your computer on the same port. If after the port forward you still have limited NAT try rebooting and than the "fix" button. (Check the extras for detailed explanation on setting up the port-forward)

📌 EXTRAS

Disable teredo (fix Rainbow Six Siege)🚫

Some games like Rainbow Six Siege, don't like teredo connection enabled, here's an easy fix, keep in mind that disabling teredo will make games that request the use of teredo not work anymore (Astroneer, Forza Horizon ...)
Run teredoFix.bat but select option 2 - DISABLE TEREDO AND REVERT ALL CHANGES

Set-up Port Forwarding 🔀

Search cmd on windows bar > open cmd > write ipconfig and hit enter > look for Predefined Gateway and Ipv4 address, save them for later (ex. 192.168.1.1 , 192.168.1.45)
Open web browser and paste the Predefined Gateway ip (ex. 192.168.1.1 or 192.168.0.1 etc...) on the top search bar and hit enter
Access your wifi router using username and password (they usually are on the bottom of the wifi router), (the password is not the same that you use to connect to your wifi).
Once you logged in search for Port mapping and than create a new rule, some routers have the option port mapping for known applications, that's the preferred option.
If you have port mapping for known applications than select it and select xbox live for windows application, than select your PC as local host, (if it asks for the ip address paste the Ipv4 you saved previously)
If you don't have port mapping for known applications than create your own custom rule:
◽ Under Traffic comming from:
You set up your interface (If you can choose between interfaces choose the one that has your public ip address in it (ussualy set by default), if you don't know your public ip address search on google "what's my ip").
If it asks: Any host = set yes
If it ask: Any port = set no, than specify port 3074
◽ Under Traffic directed to:
Host name = select your computer if there is a list of all conected devices
Host ip = paste Ipv4 you saved previously (It's the local ip address of your computer)
Port = Same port, 3074
APPLY ALL MODIFICATIONS
Wait 5 minutes (Sometimes router will take some time to apply modifications)
Reboot your computer
Open settings > games > xbox networking > wait -> it will still say teredo unable to qualify > press Check again > wait > you should have NAT open and Server Connected > if not press Fix and than Check again
If it still does not work try rebooting your wifi router and than your computer and try again to check if it worked
If it still does not work run teredoFix.bat an other time, wait for the computer to reboot and check again

Reset windows firewall 🔥

Control panel > System and Security > Windows Defender Firewall > On the left side press: Restore predefined settings

Reset your device network config 📶

Resetting your network will reset clientport and all teredo settings.
Windows 10 = Settings > Network & internet > scroll down > Network reset.
Windows 11 = Settings > Network and internet > Advanced Network settings > under the title "More settings" > Network reset > Yes.

usedToBeTomas / teredoFix