Minecraft wiki entry for Spawn, associated text: Skeletons, wither skeletons, magma cubes, zombified piglins, and blazes spawn within nether fortresses.
Ghasts spawn in nether wastes, soul sand valley and basalt deltas.
Zombified piglins and piglins can spawn in nether wastes, while magma cubes spawn primarily in basalt deltas and sometimes in nether wastes.
Ghasts, magma cubes and hoglins spawn regardless of light level.
Hoglins and piglins spawn at a higher rate anywhere in the crimson forest biome.
Endermen spawn more frequently in the warped forest biome, but not in the crimson forest.
Skeletons and ghasts spawn more frequently in the soul sand valley biome.