I have no expertise here, but if it’s mold, I’d say maybe a quick dilute bleach solution and wipe it off with a towel, then see if it has any green. If it’s dead on those branches maybe prune down to live wood?
Is it chalky and superficial that you can scrape gently away with your nail?
Maybe it’s just some residue leftover from some liquid solution that since evaporated.
Tree? Some of my scion have had that fuzz, others not. I guess depends on cultivar or growing condition. They all were fine.
Apples can have a waxy coating. I can’t tell for sure but that may be just that normal wax.
I could scrape it easily with my nail.
I’m no expert at all, but I’m pretty sure that’s normal on young shoots. I forget what it’s called tho