Although reading is good for everyone, it's particularly helpful for those with mental health challenges. Talking about the characters in books and what they face can help young people and adults deal with similar issues. It can also be used privately by an individual to work out problems they have.
The term bibliotherapy is not new but also not ancient. About a century ago, Samuel Crothers used it in an article he wrote for Atlantic Monthly.
The term is not that old but the idea of reading for therapy is as old as the Library of Thebes in Greece. Above its door, it stated, “Healing place of the soul,”
A woman named Sadie Peterson Delaney, a trained librarian. She used reading as part of the method to help Word War I soldiers who were in the VA hospital in Tuskegee.
Therapy doesn't have to just use books. It can also use short stories and picture books work as well. Poetry can also be used.
The links given here will show much more about this treatment and ways to use it.
Advancing The Youth Mental Health Conversation Through Novels, NAMI, L.M. Elliott, https://www.nami.org/Blogs/NAMI-Blog/June-2022/Advancing-The-Youth-Mental-Health-Conversation-Through-Novels
Bibliotherapy, Psychology Today
Bibliotherapy, Good Therapy
Bibliotherapy Depression Books, Goodreads
Bibliotherapy Overview, Wikipedia