I need to know before I play more as I'm going to refund this if I can't use online, I can't find any servers.

Is this just another GOG game without functioning multiplayer?

i cant find servers either also invite friends option doesnt show me a UI or overlay to send invites and even direct connect show me an error everything worked fine on early access but now is all gone on realease

Same issue here. Found other threads and reddit threads on the topic too. All had issues finding servers and connecting to friends with the GOG version.
A sloppy fix is Hamachi or similar LAN simulating software but it was an awful experience due to excessive lag and desync issues. Online multiplayer on GOG needs to be fixed ASAP.