By 'Fullbright', are you referring to the texture pack? If so, the issue may be that the pack is outdated.
If you go to the texture pack settings in-game, and the 'FullBright' texture pack has a red highlight on it, then it is outdated.
If you are referencing the term FullBright as some YouTubers may refer to, that being that the game is always lit up bright, this is in fact a texture pack. The game does not have it by default, and it must be downloaded from elsewhere.
The FullBright texture pack also requires OptiFine in order to run.
Otherwise, I am not sure what you may be referring to by FullBright. I hope this helps.
DaphlynUwU
By 'Fullbright', are you referring to the texture pack? If so, the issue may be that the pack is outdated.
If you go to the texture pack settings in-game, and the 'FullBright' texture pack has a red highlight on it, then it is outdated.
If you are referencing the term FullBright as some YouTubers may refer to, that being that the game is always lit up bright, this is in fact a texture pack. The game does not have it by default, and it must be downloaded from elsewhere.
The FullBright texture pack also requires OptiFine in order to run.
Otherwise, I am not sure what you may be referring to by FullBright. I hope this helps.