Symmetric Nat?

I can’t join any mission. How to fix this

Same too

mainly you could just make a room to see if anyone can join, or you have to fix the firewall or the router.

This is explained in the Multiplayer, i also have that

If you’re lucky enough, you’ll probably find one

Yeah, but it’s a very rare occasion.

Tried to host a game with the NAT problem:

There’s not much you can do. I will add “force port” feature in one of the upcoming updates which you can then port-forward through your router, but it will require manual configuration on your part.