[nonsporting]

John 7:15 — “The Jews therefore marveled, saying, How knoweth this man letters, having never learned?” This seems to indicate that Jesus was not formally trained. His followers called him Rabbi as a courtesy.

He was not trained by men. He is after all the Word of God.

They called him Rabbi because he was one who spoke with authority. "And they were astonished at his doctrine: for he taught them as one that had authority, and not as the scribes." Mark 1:22

[Timotheous]

Here’s another angle.
‘Authority’ here also denotes legal authority.
But the Scribes had legal authority.
So suppose the remark is meaning that ‘not as the Scribes’ refers to the content (ie ‘new’ Mark 1:27), rather than the authority. Then the comparison is not with legal authority to teach, but with the message itself.
Thanks for the debate.