"Under the sun" represents to the present sun of unrighteousness, crookedness, and vanity. (Ecclesiastes 1:2-17) There is no new creation under this sun (Ecclesiastes 1:10), but Jesus was of not of this creation (John 8:23) when he was begotten in the womb of Mary (Matthew 1:20), since his body of was specially prepared by his God. -- Hebrews 10:5.
Thus, represented in Jesus is a new sun of righteousness (Malachi 4:2), as opposed to the present sun of crookedness (corruption), which has resulted from Adam's sin. -- Romans 5:12-19; 8:20-22.
Ecclesiastes 12:7 describes the reversal of that described in Genesis 2:7. When the spirit of life is separated from the body, the person becomes a dead soul (Numbers 6:6; 9:13; Mark 14:34; James 2:26; etc.), a soul that no longer has sentiency. -- Psalm 6:5; 146:4; Ecclesiastes 9:5,10.