Granny Smith Tree Leaves Have Yellow Spots
Granny Smith tree leaves have yellow spots on top of leaf with brown, round circle, like a small growth, on underside. Leaves are dying but has apples on tree with a few of the branches also dying.
This article describes several apple problems. You may have apple scab or rust. https://www.gardeningknowhow.com/edible/fruits/apples/apple-tree-diseases.htm