When i try to use this mod on a LAN server with my brother who doesn't have the mod installed (he is using Vanilla Minecraft), he gets this error when he tries to join my world:

**Connection Lost

Unsupported (vanilla?) client!
This server requires modded client to join!**

I'm using Quilt Loader on version 1.20.1 of Minecraft.

At least with Fabric, it's only these:

[13:16:35] [Render thread/ERROR]: Registry entry (bookshelf:font) is missing from local registry (minecraft:command_argument_type)
[13:16:35] [Render thread/ERROR]: Registry entry (bookshelf:item_output) is missing from local registry (minecraft:command_argument_type)

And vanilla clients can join fine, it's only clients with Fabric API but without Bookshelf which get an error.

Hello, Bookshelf makes changes on the server that require connecting clients to also have Bookshelf installed. When you enable LAN mode you are effectively turning your client into a server and these mods will be required by all players to join.