Here is the core issue: The game relies on Steam’s Lobby system. When you click "Create Game" (LAN Mode), your PC tells Steam, "I have a lobby open." Your friend’s game asks Steam, "Are there any lobbies?" If your Steam client has network delays, firewall restrictions, or if Steam’s servers are slow, the lobby never appears.
: Use a loader like Smart Steam MU to launch the game on both PCs. Ensure each computer has a unique Account Name in the loader settings.
Here is the step-by-step process to resurrect the LAN mode.