en_tn_condensed/jer/23/40.md

But if you say ... Because you have said ... when I sent to you ... You will not say ... pick you up ... throw you ... I gave you ... insult on you

All of these instance of "you" are plural and refer to the priests and false prophets. (See: rc://en/ta/man/translate/figs-you)

I will put everlasting shame and insult on you that will not be forgotten

"I will cover you with shame that will last forever and insult that you will never forget" or "I will cause people to make fun of you forever. People will never forget that you were disgraced." Yahweh speaks of the humiliation of the priests and false prophets as if he would put shame and insult on them like clothing.

that will not be forgotten

This can be stated in active form. Alternate translation: "that will last forever" (See: rc://en/ta/man/translate/figs-activepassive)