This shaderpack has problems with the sky in some modified dimensions such as TwilightForest and Aether. When the pack is disabled, everything works fine.

OptiFine: 1.16.5_HD_U_G7
Forge: 36.2.4
TwilightForest: 4.0.546 https://www.curseforge.com/minecraft/mc-mods/the-twilight-forest
Aether: 1.0.0 https://www.curseforge.com/minecraft/mc-mods/aether-mod-1-16-port)