Is it a mod compatibility issue?

Yes

If it's a mod compatibility issue, please provide the link(s) to the incompatible mod(s)

https://modrinth.com/mod/nimble

Minecraft version

1.20

Describe the issue

Incompatible with Nimble 4.2.0 with shader activated

I only see sky from nether.
I only see white from overworld.
Still works with 1st person.

btw I changed the Nimble in jar file to be depends >=1.20.0 of mc version.
And I changed the Immersive portal version in jar from immersive-portals-3.2.6-mc1.20.1-fabric to works with mc version >=1.20.0