I have a shrub that has black spots the size of a dime. The spots are brittle and dry.
Shrub With Black Spots
Certified GKH Gardening Expert
If the spots are on the outer side of the leaves and surrounded by a yellowish looking halo, then it's most likely the result of a fungus, which can be treated with a fungicide. If the spots are on the backside of the leaves and resemble specks or dots, then it's likely caused by a pest of some sort. I would treat the shrub with neem oil, which is both an insecticide and fungicide. Here is more info: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm