So I've been trying to get this to work and I have found that I cannot create a world without the game crashing if I have optifine installed. Which is a shame cause Optifine is a near essential mod that i use to improve performance and get the most out of texture packs. I am using the latest version of Forge and Optifine. Even if they are the only two mods I have installed.

If I remove Optifine and create a world it doesn't crash but so far I still haven't successfully managed to create a world with this mod, even if I make sure its the only mod installed, as it would be stuck creating the world. It would get stuck at a 100%. I have let it sit at 100% for about 10 minutes with no change. I have tried exiting out of the game and attempting to load the world again with no changes, despite waiting another 10 minutes.

What version?

The Minecraft Version I'm playing on is 1.16.3
The version of Optifine is 1.16.3 HD U G5
The Forge version is 1.16.3 34.1.42

It is not optifine's problem, it is the mod that is incompatible with the new versions of forge, that's why it is not compatible with 1.16.4

I'm not using or even playing on 1.16.4 though,

what I mean is that the mod is compatible only until forge version 34.1.41, from then on it is not compatible with any forge version including 1.16.4

Ah I see, well that's kind of silly cause other mods I use require the latest version so that sucks. I guess I'll either have to wait for the mod to be updated or to find a work around or something or just not use the mod at all.

It's not an artificial restriction, it's a bug. It'll probably be fixed when it's updated to 1.16.4.