I only see prevention course content. Why is the library empty otherwise?

The prevention courses certified by the ZPP are visually separated from the non-certified 7Mind Plus content. You can display the non-certified 7Mind content with a few clicks in the app:

If this does not work straight away, close the app (depending on the device: double-click on the home button or press and hold the home button for a moment and swipe 7Mind off the screen) and open it again.