Hello, I have a problem with a multiplayer connection with a friend who uses a game on steam, please help
When we make a direct connection, one of us always gets an error natpunch 66 and when the public lobby is open, we do not see our lobby on the list even after refreshing multiple times, as if GOG and steam could not see each other
Problem dosent acure when i play whit my brother who uses BG3 in GOG

Weird, I don't play the multiplayer version of BG3, but my friends do, one have the GOG version and the other the Steam one, yet they finish the game together. Let me ask them if they have a problem recently or if they can try it now.
As we don't know what end has the problem, you should try to ask Larian, it has a Discord.

EDIT: They didn't have problems recently.

EDIT 2: https://larian.com/support/faqs/multiplayer-issues_84 here are some Larian recomdation, as your friend to try them too.

I got natpunch 66 errors when trying to play Baldur's Gate 3 multiplayer as well.

I was able to connect to my friend through a VPN using the Direct Connection option. Only I had to use a VPN to play, everyone else in the game was able to just connect normally.

I think this is related to limitations imposed by an ISP or router setup, not because of any differences between GOG and Steam.