Thanks for all the useful info.
UPD seems to be working fine. So I can discard this problem (no problem with `nc -vz -u 8.8.8.8 443`).
My hotspot works fine. I can use it for any other thing such as ssh, port forwarding, even watching Netflix or any usage with high traffic.
This option is harder to test, I guess that I will need to ask some guys in the lobby and see if someone is hosting a game without stun.
Currently I don't have a second computer to fully debug the issue. But thank you very much for all the ideas. If I see you online I'll ping you. Have a happy new year
EDIT: I tried to join all the games in the lobby, and for some of them I am able to join actually. So I guess that your third option probably is whats happening. I guess that I will have to see if I am able to troubleshoot this. Thanks for all the ideas!
Yes, I guess this could be a possibility. When I have a friend around with a different provider I am going to make a test. Thanks