Husks spawn at a light level of 7 or less in the desert, desert hills, and desert lakes biomes, mostly replacing zombies in these biomes.

In Java Edition, husks spawn directly under the sky in groups of 4 in place of 80% of all zombies spawned in desert biomes variants.

In Bedrock Edition, husks spawn on the surface and underground in groups of 2-4 in place of 70% of all zombies spawned in desert biomes.m

https://minecraft.fandom.com/wiki/Husk