Alright here's the video:
https://www.youtube.com/watch?v=UQ4799nHDtc TEXT GUIDE:
Make sure both PCs are connected to the same router/network
Allow the firewall access popup when booting the game for the first time, or else it might block incoming lan connections.
Go to C:/ - GOG Games - E.Y.E Divine Cybermancy - EYE - cfg folder
Copy one of the .cfg files to desktop, rename it to autoexec.cfg then move
it back to the cfg folder.
Enter this text in autoexec.cfg
sv_lan 1
maxplayers 8
Then save it, preferably have the same autoexec.cfg on both PCs so you don't have to type it into the console every time you boot the game.
Go into console with the HOST PC, type status to get your local ip, write it down
Then enter
map warp
in the HOST PC's console to host a server and start the intro hub level.
Then on connecting PCs type
connect INSERT HOST LOCAL IP HERE
Hit enter, and you should connect
I'm not sure if this entirely works, I'm not even sure if it saves characters and progress correctly, but it at least works to some extent.