Many "Anarchy" servers allow it, but competitive "Factions" or "UHC" servers often consider it a cheat because it gives you an unfair advantage in finding players or ores in the dark. Always check the server rules before installing it for multiplayer use. How to Install Fullbright 1.12.2
Many versions work on servers to help you and your friends explore together [6]. How to Install: fullbright 1.12.2 mod