ICBCLL

Increases the command block character limit to 2,147,483,647 instead of the vanilla 32,500.

If it is only present on the server nothing will change.
If it is only present on the client you can only type 267 more characters before getting kicked.

Compatible with Better Command Block UI and Command Block IDE however with these mods there will be more lag than on vanilla when a lot of characters are pasted.

Forge users: Use Sinytra Connector and Forgified Fabric API

Curseforge