When loading a world from 1.18.2, the Deep Dark biome will replace biomes in already loaded chunks. Expected is for biomes in old chunks to stay the same.

To reproduce, create a world in 1.18.2 using the seed -3945541560037994869 and immediately exit the game. When you load the same world in 1.19 snapshots and descend straight down, the locate command will show that the Deep Dark spawned in chunks already loaded in 1.18.2.