***That verse doesn’t mean every verse refers to Christ.***
Correct.
So which parts of said book are about Christ and which are not?
None.
Which parts of the book are about Christ?
There are scripturally based allegories and there are devotionally based allegories.
The first are directly stated in scripture. The 2nd are realized because of associations Christians can make with text, language, symbology, etc.
Sunrise and Sonrise are examples of devotionally based allegories. Another is “Easter” which is the direction in with the Sun rises (SonRise.)
A scripturally based allegory is the potter and the clay.
I do not recall a scriptural recognition that the Song of Solomon refers to the bride of Christ...but I am open to correction. I can see how it can be a legitimate devotional parallel.