Hi Anna-Maria,
I don't know if the Usability forum is the best place to ask this question. A moderator may wish to move it to the backup/restore or general forum.
Regarding your question: when you import a course or restore a backup, it takes the settings from the source course. If a section is hidden in the source, it will be hidden in the target.
Unhiding a section should be able using the 'Edit section' menu, selecting the Show option.
I don't know if the Usability forum is the best place to ask this question. A moderator may wish to move it to the backup/restore or general forum.
Regarding your question: when you import a course or restore a backup, it takes the settings from the source course. If a section is hidden in the source, it will be hidden in the target.
Unhiding a section should be able using the 'Edit section' menu, selecting the Show option.