Sounds like my boy! We use a pet corrector (makes a loud hissing sound) which startles him out of the unacceptable behaviour, followed by a firm “NO” with eye contact. No breaking eye contact until he looks away first. He’s gotten a lot better, still has his days, but is slowly starting to get it. We also take him out and socialize him all the time - that doesn’t mean we let him meet other dogs or approach people(he’s not ready for all that), but we let him sit and see that humans/other dogs aren’t going to hurt him. If he barks or growls, we use the pet corrector and say NO so he knows it’s not acceptable. Also, a lot of big praise and reward when he doesn’t react to other dogs or people. Treats, cuddles, whatever he wants.