Your vet could be right. Why would the dog be ANGRY? (That makes no sense.) Jumping indicates ZERO obedience training and/or over-excitement. Your dog’s reaction may also be due to a weak temperament (if you did not buy from a reputable breeder – who cared about breeding for a sound temperament) and/or it may be due to a lack of socialization to people, BEFORE 16 weeks. Just meeting or being with your family is 100% inadequate socialization, to other people.
With Covid being a problem for the last 7-8 months many dogs (obtained as puppies during this period) DID NOT get good socialization as puppies, either in your home yard or out in the world with friendly, dog savvy people. Further, very few dogs ever got into any puppy kindergarten or basic obedience classes where they could have been socialized and exposed to BOTH people and dogs. So now we see lots of nervous anxiety ridden dogs – who cannot COPE with the world.
If you vet is right, was your dog EVER fine or even friendly with people getting in the elevator after 4 months of age? Did anything change – aside from the masks? Most people started wearing them in March. Yours is the first complaint I’ve seen – *if* the mask is the total ISSUE. (Personally, I do not think it is.)
Sadly, there are lots of issues here. I would NEVER have recommended a GSD for anyone in an apartment. GSD are only a good pet for the very experienced dog handler. They are a high energy and protective WORKING breed (by nature) and usually bark too much at sounds in such a tight living situation, and need more exercise, than can be easily provided by walking. Many apartments WILL NOT ALLOW the breed, as it is on many “dangerous breed lists” due to the protective nature of the breed. I DO NOT consider well-bred GSD to be danger in public – to anybody, but yours is making a different case, right now due to fear or anxiety.
Hire a trainer or animal behaviorist (ask your vet for referrals) to help you both evaluate the dog, and then desensitize the dog to people and to help you start obedience training – which ALSO BUILDS CONFIDENCE in shy or fearful dogs – as well as giving you more control. Your dog can also easily sense your uneasiness – it goes straight down the leash, so as you ANTICIPATE or worry there will be a problem – you will get EXACTLY THAT. If you are IN FULL CONTROL, you will worry less.
For now => ASK anyone else waiting to use the elevator, to either go w/o you, or to allow you to go ALONE on the elevator (also consider using a MUZZLE) so the dog cannot bite anybody, OR you (PLURAL) need to start using the STAIRS.
IMO, you need to move to a rental HOUSE, in the long term, esp if you & the trainer do not get this FIXED. Nobody should be threatened or terrorized by a dog in an elevator. I have shown a Germanic breed for years & stayed in many motels/hotels and NEVER had my dogs react badly to either the elevator movement or to anyone -who got on WITH us. This ought not to be happening, but there is obviously a disconnect.