BlueStaggo

The issue is found in this area in the code: https://mcsrc.dev/1/26.2-pre-1/net/minecraft/data/worldgen/SurfaceRuleData#L259

Removing the frozen ocean check is very simple:

Ok yeah I checked an assets repo and they do have new sounds and they didn't get downloaded for me. Darn it. Mojang is so unpredictable.

I have released a resource pack to fix this: https://modrinth.com/resourcepack/restored-brightness

But at the same time, surely this is a bug. Seems like the lightmap itself have the right color values but something is screwing up with the sky light.

Yeah, you're right, it's a duplicate and it works as intended. I'm going to attempt to make a mod to fix this.