Minecraft 1.16.5
Latest Optifine
Multiple Shaders tested
Astral Sorcery-1.16.4-1.13.9

I figured that it's a skybox bug
here is the result: https://imgur.com/a/nuyPe0i

I assumed it could be fixed in config but I'm not sure how.
Thank you.

Astralsorcery-client.toml has the options needed to disable/minimize the AS sky render. Shaders aren't supported, so it's the closest you can get.

Can you give me an example on how to disable it. I'm not very good with this sort of thing.
Edit: just a photo of sorts showing what the toml would look like

I woyld recommend reading the entries, there are only 4 or 5 in that file, then visiting the discord for assistance after that. It is the more appropriate forum for non-bug assistance.