Lain402 Many DSLR manufacturers do not open up the camera control API so everything has to be reverse engineered and by far the best option is to use gphoto2. Coming back to your question if it is so hard to support the Z6 and Z6II: yes it is! Complain to Nikon for not opening up their APIs for software developers instead of blaming other developers.
So, the question remains: are the Z6 and Z6II supported by gphoto? If yes then report that here so ZWO can add those cameras to AAP.