While does not have a dedicated "offline" LAN mode, you can play together on the same local network by using the standard multiplayer interface. However, this often requires specific fixes to overcome common connectivity and desync errors (like LR40 or LR39). Essential Connectivity Fixes
Ubisoft’s online services still try to route LAN traffic through their relay servers. The game doesn’t reliably fall back to direct IP / local broadcast. anno 1800 lan multiplayer fixed
Clear the Sync Cache: Delete the Sync Data folder located in your Ubisoft Game Launcher directory (usually AppData/Local/Ubisoft Game Launcher/cache/http2/Default). All players should do this before restarting the game. While does not have a dedicated "offline" LAN
You can have up to 16 players in total, divided into 4 factions. Crossplay: The game doesn’t reliably fall back to direct
Even if you are in the same room, the game still pings Ubisoft's servers.
Multiplayer will fail to load if there is even a minor version mismatch: Mismatch problems multiplayer guide for Anno 1800 - mod.io