jumia,
If I understand you correctly, you wish to add more than one playlist from Qobuz to play in the App. You can do so. The left hand list you see is the active loaded music to play. When that list plays through or you tire of that assortment playing , you can press the trash can icon on bottom of the list and you get prompt asking if you wish to clear the playlist. Selecting Yes does not trash your Qobuz Playlists, only clears the active selected music. You can also add music to the active playlist from your Qobuz Playlists and/or music from your stored files. Essentially you have control to edit and create custom playlist in the App. You can clear that or if you wish to save that playlist, you select the edit button (far left button) at bottom of the play list. It will prompt you to name it and save it. To see these App saved Playlists, select the music note icon on the bottom of the playlist. You can then select that playlist to play with the window that opens with note icon, download icon gives option to overwrite and save modified playlist where you may have added or deleted music to the playlist or save to your Qobuz playlist.
If you want to add additional music to listen to from your Qobuz playlist, you can do so even while your first selection is playing. To do so, open your Qobuz playlists shown in the App and press down on the playlist you wish to add. The screen will show an arrow on top of file icon which immediately adds new playlist to begin playing, the arrow inside of file will insert the playlist into the order of the active playing list, and arrow at bottom inserts additions at end of current actively playing music.
I strongly suggest taking some time to experiment with the App. It provides you wide choices including just temporarily playing selections to saving as customized playlists within the App. I think once you get some experience with the options, you will change your current view of it.
Good luck.