'then they are able to see all the courses, not only the courses they are enrolled.'
That's not correct Fernando. If the front page setting to show Enrolled Courses to logged in users is selected then that is what will be shown (as per my screenshot above) - there is another option for showing All Courses, which will - as it says - show all courses irrespective of the ones enrolled.
@Nadirshah, Have you perhaps given the user the student role across the whole site, rather than in individual courses? That would probably cause them to show up with all courses listed as they will have the student role in all courses.
You can check by enabling both the Enrolled Courses and the All Courses options in two separate drop downs of the 'Front Page when logged in' setting I showed earlier.
But Fernando is right - this is not a theme issue, Adaptable works exactly the same way as Clean, Flexibase, Essential and every other theme in this regard (just tested - Enrolled/All Courses show up separately and as expected based on the front page settings).