[anonymous]

The first thing I would do would be to take him to the vet for a checkup and discuss medication that’s prescribed for separation anxiety.
Especially because you have a large breed that could become aggressive and bite someone (fear aggressive).

Some of these medications take a week or two to start to be effective, at that time he may become calmer, less fearful therefore becoming more receptive to training and being around other dogs and people.

However, he may always be a bit shy, some of what you are observing may be his personality. Just like people, some dogs can be introverted.

From a previous post (use search engine to look up “anxiety”)
“Medications were invented for a reason, when used appropriately under the guidance of a veterinarian and in conjunction with desensitization and gentle training techniques. they can be very helpful in decreasing anxiety levels therefore making the dog receptive to learning and getting over fears”.

“They are also very reasonable, especially when compared to dog trainers and such.
Example, Clomicalm was prescribed for a dog I had years ago, she only needed to be on it a few months”
“Excellent results. The dog never appeared sedated, she was alert, no change in personality noted, except for being less fearful. Some medications take up to a week or two to show effect, discuss with your vet. There are other medications to choose from now. Your vet will help you evaluate if this is an option for your pet”.

‘Clomicalm is a tricyclic antidepressant (clomipramine) that’s used to treat separation anxiety in dogs as part of behavior modification plans. Clomicalm makes it easier for dogs to learn new, positive behaviors. By easing anxiety caused by separation, Clomicalm controls destructive behavior, vocalization, and other negative behaviors’.
(above copied from vet depot dot com)

PS: Don’t be fooled by supplements, flower drops, etc. They don’t work.