If this is the one apple tree of others that are unaffected then it's probably not a frost or freeze. If the whole tree seems suddenly sick or even dead then that's a new one on me. It does look kinda "blighty" though. Is the tree in a pot? A new/young tree?

It has been in it's current pot for about a year. I have had the tree for 3 years. I think it was a 3 year old tree when I got it.

Does not look like fert burn ...which would be hard to do anyways with organic fertilizer unless you really went overboard.

I have 3 semi-dwarf apple trees (in ground) which are about 14 YO now, they are all about 15 ft tall and 12 ft wide today. Being confined to a pot may put an upper limit on their lifespan? Have these produced fruit yet?

It hasn't since I got it. Last 2 years we had killing frosts on blooms. I set some pictures to our local Extension office, so hopefully they can help me out.

I am beginning to wonder if it is some sort of fungal infection that overwintered. I do remember some of the leaves last year having black/brown spots and yellowing at the end of the season. I thought that was stressors related to the European Hornets that were girdling some of the branches, who knows. I am going to move the tree far from the other in case it is contagious.

Just an update, about a week ago I noticed a ton of little pin holes with frass coming out. Seems like shot hole beetles/fungal infection were perhaps the cause. I ended up burning it down.