Minecraft wiki entry for Pillager_Outpost, associated text: In Java Edition, only pillagers and passive mobs may spawn within a pillager outpost spawn area. Pillagers may spawn on any valid opaque block as long as the sky light level is 11 or lower, and the block light level is 8 or lower, but can also spawn on grass or sand blocks regardless of sky light level. Therefore, players may pacify an outpost by removing all grass/sand blocks and properly lighting the area as they normally would to prevent enemy mob spawns.