Can't play a game with my brother

We have two computers. 2 cables connected through one router. IP Adress from provider is dynamic and didn’t have blocked ports. Purchased 2 copies of the game for 2 Steam accounts.

When two of us connect to the server, one of us disconnects from the server.

We tried VPN, it doesn’t work. We disabled the firewall - that doesn’t work either.

I reinstalled Windows and deleted the game account with 86 falconer in order to create a new one - this also did not help.

When one of us plays alone, everything is fine, if we connect together to the server, it’s a disconnect.

I have already sent a ticket to support and I am sure that they will answer me in a million years, so I want to ask people - who also experienced this problem? Is there a solution?

It’s very disappointing that we spent money on two copies, but we can’t play together. This is complete nonsense