Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Maltese, watch their eyes, their energy and their growth. A squint, or discharge that changes colour, needs looking at. A young Maltese who goes weak or very sleepy may have low blood sugar: contact your vet now. If a puppy grows slowly, contact your vet the same day. A first seizure, one that lasts more than two minutes, or more than one in a day is an emergency: contact your vet now. So is bloat (GDV, a twisted stomach): a swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling. It can happen in any dog, though it is most common in large, deep-chested breeds. From middle age, a cough or faster breathing while they sleep can be their heart.
You'll keep filling your phone. If one of the photos shows a squint, tell your vet.