The nether actually already had fog before 1.16. Optifine kinda sucks actually and is really only allowed pre 1.15 because there aren't really any better alternatives Okayge

Dangerousfourteenthousandfifteenone

Something along the lines of: optifine changes the way the world loads and how mobs spawn

But no optifine in 1.14+ glitched categories

No, you are not allowed to use any launchers. The only things you can use are optifine for pre 1.16 and sodium/phosphor/lithium for 1.16.