I was trying to connect with my friend who has the steam version and we are getting the NATPunch[66] error. I was trying to solve It by forwarding ports 23253-23262 and 23243-23252 on my router with uPNP enabled as support suggested, but so far with no success. We have the same version. If anyone found a solution please let us know. Or is this simply a known issue that Larian must fix?

https://www.gog.com/forum/baldurs_gate_3?search=NATPunch

OK so after many tries. We were able to get together with another friend.
But the sequence was super strange. The main issue we found is, that the two of us are on the same ISP in small town and we do not have public IPs. We were able to connect with hamachi, but had a lot of lag, basically unplayable. So we invited another friend on different ISP to try It that way. He has a steam version, so he had no problem connect with my other friend, but again I could not join. In the end I and the friend on the different ISP joined using hamachi and he then invited the third friend from the same ISP and then we could play without an issue. But oh man I didnt expect to having the same trouble in 2023 as we used to have in 2001 :).