Hello. Happy to help.

The photo is not very clear nor close enough to the spots for me to determine what that is but one thing that is commonly found on the bark of maple trees is lichen. If it is lichen, they are not harmful to trees. Here is more information about lichen on trees: https://extension.umn.edu/trees-and-shrubs/non-harmful-tree-conditions

I did notice the leaf in the lower left corner that appears to be chlorotic. There can be many reasons for chlorosis. This is caused by poor absorption of nutrients in the soil be it from high alkalinity of the soil or a root that's strangling the trunk.  I would suggest getting a soil test to ensure it isn't the pH or lack of soil nutrients that's causing the problem. Aside from that, I have a few questions that may help us figure out a possible cause.

1) Are the chlorotic leaves on one side of the tree or the top or just the bottom branches?

2) Do you irrigate the tree or do you leave it to mother nature?

A photo of the full profile of the tree and a closeup of the base of the tree would also help.

Check out this link to the U of MN Extension soil test page where you'll find out about the service, price, and how to submit a sample for testing.

http://soiltest.cfans.umn.edu/

I look forward to your answers and additional photos.