Issue:
Attempting to create a new world causes a crash due to a missing server config file (path: [world save folder]\serverconfig\lantern\config-server.toml).

Versions/mods present:

• Client: MultiMC 5 v0.6.12-1530
• Minecraft 1.16.5
• Forge 36.1.31
• InfinityLib 2.0.6
• Lantern 2.0.3

To recreate the issue:

• start the game
• enter singleplayer, create a new world (any world settings are fine)
• once world creation starts, the game will soon generate a crash report and then hang indefinitely until forcibly closed by the player.

Additionally, though testing was performed in singleplayer, the crash itself is caused by the absence of a server-related file. Therefore I would guess that the issue also affects multiplayer.

I have also linked a crash report for better analysis: https://pastebin.com/YuwMde12

Might be a Forge issue: MinecraftForge/MinecraftForge#7963

Try updating Forge to check if it has been fixed?