I think Mamuang is probably right and the tree has Alternaria Leaf blotch. It’s possible its frogeye leaf spot looking at the last picture but I think that is unlikely. This is due to the large masses of brown on some of the leaves which are associated with Alternaria Leaf blotch. You don’t have fireblight or powdery mildew for sure. I don’t think it’s scab either. It could be something else but the remedy is going to be the same you spray with a fungicide to prevent the disease.
You’re going to want to spray the trees in the future. For this year it’s a judgement call you may spray or skip it since the blotch is pretty well established. I would certainly start spraying next year.
I would start with one of the two spray schedules that we have on the forum. We have an organic spray schedule provided by Scott which is very detailed but don’t let that scare you. Basically, you spray sulfur in the Spring and after petal fall you spray sulfur mixed with Surround or Spinosad. Alan has authored the synthetic spray schedule. Here are links to both below.