As some people recommended in this forum, you may consider taking the courses from Dominik Cebula from Udemy.
Those courses are pretty helpful. Dominik went through the exam objectives in depth.
If you study hard in his courses, read the books recommended by the other people, you should be good.
There is no one set of mock exam that match with the difficulties of the real exam.
So, we have to rely on courses , books , Spring's official documentation and mock exams.
On average, it takes people from 9 months - 16 months to prepare for this exam.