Aggressive puppy

Hi! I recently adopted a 10week (now 12 weeks) old puppy from a shelter. He’s a mutt but we think he’s got Pitt in him and maybe golden? It’s unknown. But he’s become aggressive. Not normal puppy biting but he will fully snap at people spontaneously. He was given a treat by my step father and after eating it he attempted to pick him up to which resulted in him getting bit multiple times. Im a female and he allows me to pick him up with no issue. He absolutely hates men and will bite any man that tries to pick him up and will also nip/bite and growl at people just for being near him. He was playing with my young cousin and decided he was done playing (totally fine and normal) so he laid down. My cousin then went to pet him and he tried to bite him. We thought it was just men but he will spontaneously go after any and anyone. Any advice? Is this fear aggression, insecurity, etc?