The phrase the son of man apart from Jesus
Psalm 8:4 - “What is man that You take thought of him, And the son of man that You care for him?”
Psalm 80:17 - “Let Your hand be upon the man of Your right hand, Upon the son of man whom You made strong for Yourself.”
Ezekiel 2:1 - “Then He said to me, “Son of man, stand on your feet that I may speak with you!”
Ezekiel 2:3 - “Then He said to me, “Son of man, I am sending you to the sons of Israel, to a rebellious people who have rebelled against Me; they and their fathers have transgressed against Me to this very day.”
Ezekiel 3:1 - “Then He said to me, “Son of man, eat what you find; eat this scroll, and go, speak to the house of Israel.”
Job 25:6 - “How much less man, that maggot, and the son of man, that worm!”
Daniel 8:17 - “So he came near to where I was standing, and when he came I was frightened and fell on my face; but he said to me, “Son of man, understand that the vision pertains to the time of the end.”
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Jesus as the Son of man
Daniel 7:13-14 - “I saw in the night visions, and behold, one like the Son Of Man came with the clouds of Heaven, and came to the Ancient of Days, and they brought him near before him, A and there was given him dominion, and glory, and a kingdom, that all people, nations, and languages should serve him, his dominion is an everlasting dominion, which shall not pass away, and his kingdom that which shall not be destroyed.”
Matthew 9:4-6 - "And Jesus, knowing their thoughts, said, Wherefore think ye evil in your hearts, for whether is easier to say, Thy sins be forgiven thee, or to say, Arise and walk? but so that you may know that the Son of Man has authority on earth to forgive sins”—then He *said to the paralytic, “Get up, pick up your bed and go home.”
Matthew 26:64 - "Jesus said to him, “You have said it yourself; nevertheless I tell you, hereafter you will see the Son of Man sitting at the right hand of Power, and coming on the clouds of heaven.”
Mark 2:10-11 - “But so that you may know that the Son of Man has authority on earth to forgive sins”—He *said to the paralytic, “I say to you, get up, pick up your pallet and go home.”
Mark 8:31 - "And He began to teach them that the Son of Man must suffer many things and be rejected by the elders and the chief priests and the scribes, and be killed, and after three days rise again.
Mark 14:62 - "And Jesus said, “I am; and you shall see the Son of Man sitting at the right hand of Power, and coming with the clouds of heaven.”
Luke 5:24 - "But, so that you may know that the Son of Man has authority on earth to forgive sins,”—He said to the paralytic—“I say to you, get up, and pick up your stretcher and go home.”
Luke 9:22 - "saying, the Son of Man must suffer many things and be rejected by the elders and chief priests and scribes, and be killed and be raised up on the third day.”
Luke 22:69 - "But from now on the Son of Man will be seated at the right hand of the power of God.”
Acts 7:56 - "and he said, “Behold, I see the heavens opened up and the Son of Man standing at the right hand of God.”
Revelation 1:13 - "And in the midst of the seven candlesticks one like unto the Son of man, clothed with a garment down to the foot, and girt about the paps with a golden girdle.
My take on this subject is simple and uncomplicated. The Old Testament verses presented refer totally to all mankind but Jesus due to his unique position as the God/man. When “the Son Of Man” appears as shown in the scriptures whether Jesus speaks those words or not refers to only one person since the word “the” is singular and allows no other than the object referenced by the word the.
For an example; in the Old Testament verse Psalms 8:4 the son of man refers to mankind not a single individual as proven by the part of the verse that says, “What is man (mankind) that you take thought of him?” It follows the son of mankind would apply to all sons of men.
In reference to Daniel 7:13 – “The Son of Man” has to refer to Jesus based on verse 14 and references to his dominon, glory and kingdom being everlasting and not passing away. It would require some stretch of imagination to think it could mean all mankind since the only person in scripture that has an “everlasting kingdom” is Jesus himself. I believe a thorough search of scripture will conclusively prove this point.