In general, cracking your back (or adjusting your back) is not bad if done correctly, but it’s probably not fixing the issue causing the back pain. These back stretches & exercises target muscles that often cause back pain.
If you have certain diagnoses, you should not crack your back, so these stretches and exercises are a better alternative.
Bridges are a great way to start to loosen up your back and hips.
Stretches like single knee to chest, supine trunk rotation, and lower back stretching with a leg cross over will help relax tight back muscles that might be causing your back to be out of alignment.
Isometric exercises are a great way to not only strengthen your muscles, but also help adjust your joints if needed. Muscle energy techniques (MET) help to do this.
Finally, prone props should only be done if you know what your diagnosis is. They are good for disc issues, but not other ailments.