Change brightness to 90 to have fullbright full.
Provides Full Visibility:
Fullbright mode illuminates all areas in the game at daylight levels.
Eliminates the Need for a Light Source:
It eliminates the need to carry a torch or other light sources to find minerals such as diamonds, coal, and iron.
Provides Ease of Construction and Exploration:
It allows movement without being affected by darkness while building structures or exploring new areas.1.21.8 Fullbright Texture Pack is a free Minecraft Java resourcepack. Downloaded 113,200 times. Download it and open it directly in the game.