Hostile mobs no longer are able to spawn during daytime in Dark Forests compared to 1.16 and 1.17 versions.

This is not a misconecption about mob spawning they simply are unable to spawn under the Dark Forest canopies even when block light is 0 while they can in 1.17.

Steps to reproduce visit Dark Forests during daytime in 1.18 and 1.17 and compare.

Or make mob spawning area with ceiling made out of Dark Oak leaves and see the difference during daytime between 1.17 (mobs spawning) and 1.18 (mobs don't spawn at all)