Well, sad story. Looks like this ticket/task will be forgotten and buried as 999x other such tickets related to the launcher.
And as usual, it's just a "Feedback" for BI rather than real problem..

Ffs.. Where is the problem to implement the server list fetching logic in a same/similar way DZSA did?
They are crawling servers from the Steam API (https://api.steampowered.com/IGameServersService/GetServerList/v1/) which cannot be spoofed that easily as direct A2S queries.

@Geez Hi, any ideas regarding this?

In T181542#2694264, @Geez wrote:

Hello BGZ,
We will require more information as to how are you connecting to the server?

@Geez This clientPort setting/option would be really helpful in order to configure server firewall to not allow any incoming connections from different ports.
Any ideas when this could be fixed?

Hello,
Seems like this still is an issue..
I have tried to set different ports in clientPort, but client just ignores that (looked through Wireshark).