How to make a pressure plate output redstone given condition.

do you want it to increase the more of them it has?

If your using a custom block, there should be a trigger called "When Enity Walks On This Block" put your procedure on that one, and use a IF statement that reads IF Event/Entity is creature type 'Undead' > then do your logic. Alternatively you can type in the search box "sub" and a block should come up named "Is Event/Entity (sub)type" and that will allow you choose a specific type of mob.

This code should be what you want.

public class LaunchAtHeadpointingProcedure {
	public static boolean execute(LevelAccessor world, double x, double y, double z) {
		boolean undeadPresent = false;
		undeadPresent = false;
		{
			final Vec3 _center = new Vec3(x, y, z);
			List<Entity> _entfound = world.getEntitiesOfClass(Entity.class, new AABB(_center, _center).inflate(1 / 2d), e -> true).stream()
					.sorted(Comparator.comparingDouble(_entcnd -> _entcnd.distanceToSqr(_center))).collect(Collectors.toList());
			for (Entity entityiterator : _entfound) {
				if (entityiterator instanceof LivingEntity _livEnt ? _livEnt.getMobType() == MobType.UNDEAD : false) {
					undeadPresent = true;
					break;
				}
			}
		}
		return undeadPresent;
	}
}