When I try to use any shader, the sky appears pure white in the day, and shows a weird line above the horizon during sunrise, sunset, and nighttime.

Which shader is that?
I just tested the same thing using Complementary shaders and, apart from the new Skyweave block not rendering as expected, I faced no such issues.

And also, are you running Rubidium & Oculus, or Optifine?

I have the same Issue on the same version

Im using optifine

Same issue here, optifine also, moon and sun just seem bugged, all shaders just seem very off

I am using Optifine with Complementary Shaders and have the exact same issue!

Is there anything in the log file? Optifine is closed source so this is pretty difficult to figure out.

Exact same issue here
OptiFine_1.19.2_HD_U_H9
Forge 43.1.1
BSL Shader

@SammySemicolon I have no idea what I'm looking for, but I found two lines which stood out to me:

[22Feb2023 02:44:47.116] [modloading-worker-0/DEBUG] [net.minecraftforge.fml.javafmlmod.AutomaticEventSubscriber/LOADING]: Auto-subscribing com.hollingsworth.arsnouveau.client.SkyTextureHandler to FORGE
[22Feb2023 02:44:47.117] [modloading-worker-0/DEBUG] [net.minecraftforge.fml.javafmlmod.AutomaticEventSubscriber/LOADING]: Auto-subscribing com.hollingsworth.arsnouveau.client.ShaderRegistry to MOD

Is this information of any value?

No not really. Those 2 classes handle the sky rendering yeah, but I already know that.

I have the same issue when using Complementary shaders
(Forge 43.2.0, Optifine 1.19.2 HD U I1)

I have the same issue with Sildur Vibrant Shaders, Optifine 1.19.2 HD U I1 Forge 43.2.6, the sun and moon both have black squares around them and I can see both at all times through the floor. The issue disappears when it's cloudy/raining. I've tried looking for a sky option in the configs but I'm not very code savvy (my apologies), and could not find any. Is this something we can edit in a file somewhere?

I too am also having issues with this mod and Complementary Shaders. I'm using Forge 43.2.0, Optifine 1.19.2 HD U I1, and Complementary Shaders 4.7.1. No other mod I'm using has issues and running with just those 3 enabled has no issues, yet when I turn on Ars Nouveau it breaks.

It's definitely a conflcit between ars noveou and optifine.
With iris/oculus, the end result is the skyweave block not rendering at all.
Really not sure how to go about fixing this- I tried a whole bunch of minor tweaks to the code responsible for this whole array of issues, ranging from tiny changes to ripping crucial parts of the code out- without the know-how on OptiFine, it's hard to do anything.
Having ars-noveou turn off the skyweave rendering (since it doesn't work anyway) when OptiFine is present and shaders are enabled might be the best course of action.