I need help with Forza Horizon 4 Online?

I bought Forza Horizon 4 on my PC and now I want to play online because I've played the game so far that I can play it but it just doesn't work. The Xbox app says something is wrong with the Teredo filter. I have a FritzBox as a router and have already deactivated the Teredo filter there. Now I don't know what to do next.

I had that too. You have to switch off the teredo filter in the router settings and then look again. If it still doesn't work, take a look at yt n tutorial. You can also update or restart your Fritzbox

The FritzBox is up to date and as I said, I've already turned off the filter and I've already spent hours on yt and they always do the same thing and that doesn't work for me

https://support.xbox.com/...party-chat