How?

When approached by a Piglin Brute, With Optifine and Shaders equip, I noticed the Piglin Brute was invisible, and because of this it killed me and pushed me into the Lava, Please get onto this. Another thing is, if you load Minecraft: Java Edition 1.16.5 Optifabric, with fabulous equipped it makes all or many mobs go invisible. Please fix everything specified.