Features of the Gospel of Mark
The Gospel According to Mark has the following features:
People were saying, "[Jesus] has gone out of his mind" (Mark 3:21).
Only place in the New Testament Jesus is referred to as "the son of Mary" (Mark 6:3).
Mark is the only gospel where Jesus himself is called a carpenter (Mark 6:3).
Only place that both names his brothers and mentions his sisters (Mark 6:3).
The longest version of the story of Herodias' daughter's dance and the beheading of John the Baptist (Mark 6:14–29).
Customs that at that time were unique to Jews are explained (hand, produce, and utensil washing).If any Apostle or Disciple had written this Gospel or an underlying document of this Gospel, the above features should not have been observed.
https://en.wikipedia.org/wiki/Gospel_of_Mark#Comparison_with_other_writings
It was written by someone who could write delicate incidents related to Christ Jesus without a fear of provoking Him, who knew very details of the family members of Christ Jesus, and who had strong affection for John the Baptist. Accordingly, this Gospel must have been based on a report written by Christ Jesus Himself after the Resurrection.
Or could any Apostle or Disciple who believed that Christ Jesus was God or the Son of God write that He had been a carpenter who had been once said to have gone out of mind?
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Mar 9:17 And one of the multitude answered and said, Master, I have brought unto thee my son, which hath a dumb spirit;
Mar 9:18 And wheresoever he taketh him, he teareth him: and he foameth, and gnasheth with his teeth, and pineth away: and I spake to thy disciples that they should cast him out; and they could not.
Mar 9:19 He answereth him, and saith, O faithless generation, how long shall I be with you? how long shall I suffer you? bring him unto me.