Looks like scale.

Yes, it's powdery mildew. Very common issue with some types of apples.

thank you for your answers. Maybe that’s right. I’ll try to spray with diluted baking soda after this raining week to see if that works.

You may find a lot of the powdery substance is gone after a good rain. Powdery mildew spores are actually discouraged by contact with water. And can be rubbed off gently with your fingers.

For a young tree I might consider treating if the infection is severe. For a mature tree, the PM is more cosmetic in its impact than harmful and generally requires no treatment.

That’s good to know. It is a mature apple tree. I’m glad it’s nothing to worry about. Thank you gardengal48

Gravenstein apples are my most favorite and almost impossible to find in a grocery store. But the tree is highly susceptible to both powdery mildew and apple scab. However, I was able to grow a large and otherwise healthy tree with plenty of completely edible fruit without ever spraying. It would experience some early leaf drop because of these issues but not enough to weaken the tree or seriously alter its appearance.