You cannot use optifine for 1.16+

idk but just ask in the same thread

Please do not use any mods unless they are necessary to increase performance. Until an acceptable alternative is found or developed, Optifine is allowed for versions from 1.0 through 1.15. If Optifine is used: No Fast Math No Clear Water No Dynamic Lighting No Lazy Chunk Loading Render distance must be a value allowed by Vanilla on the Minecraft version you’re playing No disabling fog No shaderpacks No using Optifine zoom No disabling explosion particles No disabling animations

it handicaps mob spawning (less mobs spawn)