Unlike older Paradox titles, CK3 uses a hybrid networking model:
Let’s get the hardware out of the way. Nothing kills a LAN party faster than desync errors on the eve of the Crusade. ck3 lan multiplayer
You have the cables. You have the snacks. Now, how do you actually start the CK3 LAN Multiplayer session? Unlike older Paradox titles, CK3 uses a hybrid