Is OptiFine allowed?


you can only use it for pre 1.15. 1.15+ is banned because it changes the behavior of the vanilla game and these features are non-vanilla unlike optifine 1.14-1.0 which doesn't change it and can easily disable these features if you are using 1.14-1.0 read the rules for optifine
but if you are using 1.16+ use the mods here

BigLadMuzzaBigLadMuzza, PoisonousSkelyPoisonousSkely and 2 others like this. 

1.16+ you cant


Only if you need h to e performance enhancement like if you are using a laggy computer/pc


^ this is incorrect

BigLadMuzzaBigLadMuzza and TuttereyTutterey like this.