Ecclesiastes and the Song of Solomon

The book of Ecclesiastes gets its name from the Greek word for "congregation", but the Hebrew title refers to the teacher or speaker to the congregation. The teacher was possibly Solomon, and if so, it was likely written after he traded his wisdom for a huge harem of foreign women, and possibly after repenting. Its theme is the futility and meaninglessness of mortal life. All the teacher could conclude is that meaning is found only through faith in God and living accordingly.

The Song of Solomon (or Song of Songs) could have been written by someone other than Solomon, possibly even a woman, since it seems to be more from the woman's perspective. That is, "Solomon's Song" could mean the song ABOUT him rather than BY him. It's written as drama or at least a vivid love poem.

Resources:
commentary https://www.studylight.org/commentaries/eng/dcc.html