Q.What Is Infecting The Leaves On My Viburnums?
I noted white (roundish) growths on the underside of a number of leaves of my “blue muffin” viburnums. They line up at the joint of the veins. On the top side, they show as linear bumps along the main vein: the leaves curl up some on the edges. I don’t know what this is but I will try to attach photos of these visitors. I couldn’t seem to get a photo of the topside due the leaf curling. It is hard to get a clear photo of this invader.

Certified GKH Gardening Expert
Unfortunately, your photos are blurry. If you cannot get a clear picture on auto, you will have to adjust your focus, manually, to the lowest setting. Or you can take a picture further out, and crop the photo to the pest in question. This will produce a more clear photo.
In the meantime, a broad spectrum insecticide will be a good starting point. These articles will help:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides