Why is Dome light staying on aftr I start car? It only turns off when I shut door & lock it

This light is a "courtesy" light. If your door is open, the courtesy door ajar switch is not engaged, on this vehicle, the door switch will not engage the dome light to shut off until the doors have been locked. If you have had the door lock assembly replaced already it may need programming as well (not all need programming). You can have this done at any Porsche dealer for a fee