My acer palmatum which I’ve had for 5 years has developed cream coloured spots all over.

Question

It’s in partial shade. The soil is clay.

Answer 1

Japanese maple leaf problems may look like trouble, but that’s about it! Typically, they don’t affect your tree’s health.
Usually leaf spot, anthracnose and powdery mildew can be cleared in a few steps.
Avoid getting water directly on tree leaves (by overhead irrigation) because fungi thrive in wet conditions.
If your tree does needs watering, water in the morning, so they have the whole day to dry.
Rake up infected leaves in the fall until the tree’s bed is completely clear.
Bag ’em and send them off with your garbage collection. Don’t compost, or you risk spreading the fungus spores all over your yard.
If any branches or limbs look dead, prune those out using proper pruning cuts.
Fungicides aren’t necessary for leaf problems. If you want the extra safety net, your arborist can recommend treatment.
https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maple-tree-lifespan.htm