Looks like the entire center vent unit pops out. There are no screws holding it in. 22 and 23 have to do with cupholders.
Call Porsche dealership and find out exactly how you pop it out.
Or if you have lots of DIY experience with stuff, get two mini pry bars (look like screwdrivers with curved tips) protect dash with leather pieces under pry bars and see what happens (SEE WHAT HAPPENS DO NOT FORCE - proceed only if it looks like it's coming out when you apply MINIMAL force. If there's ZERO way of using the pry bars without causing visible damage to unit then don't even try. I do investigative stuff like that all the time. The trick is to know when it's not going to work WITHOUT damage. Many times you have to give up.