LuneOS tries to keep webOS alive

webOS is a gesture-based interface. The single button you describe is actually a marker for the centre of the gesture area. Place your thumb there and slide it to the left. This is the 'back gesture'. If enabled, swiping the full width switches directly between cards without needing to go via card view. Swiping up from the area brings the 'wave launcher' of the quick launch bar, but I don't know if this is yet implemented in LuneOS. Tapping or swiping up takes you to the card view as you have found. A swipe up here brings up the app launcher pages.

Hopefully, you will now enjoy the experience more! ;-)