Passe a string de pesquisa inteira como parâmetro para o operador LIKE :
results = db.execute(text("SELECT * FROM books WHERE title LIKE :search"),
{"search": f"%{search}%"}).fetchall();
ou, alternativamente, concatenar no banco de dados:
results = db.execute(
text("SELECT * FROM books WHERE title LIKE ('%' || :search || '%')"),
{"search": search}).fetchall();