Leaves with brown spots falling off tree
Leaf spots are very difficult to ID, but I think this may be bacterial leaf spot. This is usually treated with a copper or streptomycin based spray. Here is info from the U: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/management-of-leaf-spot-diseases/#bact...
Given the size of the tree, you would probably need a certified arborist to do the spraying. Other management strategies you can do are detailed at the end of the information in the link above.