Motivated by the issue description here: https://github.com/ValveSoftware/Proton/issues/3189#issuecomment-2303407967 .
I didn't check anything with the game, but provided example shows the difference between Windows and Wine behaviour. I don't see Win11 specifics though, the tests I added so far seem to work on all the Testbot versions (while locally I am testing on Win11). The interesting bit however is that sendto() with given address is not allowed without SO_BROADCAST on Windows too, this "SO_BROADCAST" bypass works only when connect() is used on udp socket to attach to broadcast address and then send() without address. It works in a somewhat similar way on Linux. Unlike Windows, SO_BROADCAST is required to be set for connect to succeed. But when connect is performed send() without address will succeed even with later disabled SO_BROADCAST. I verified locally with Wireshark that it is not just success status, the broadcasts are actually sent over network when running included tests both on Windows and Wine with the patch.