For those the like tinkering, here is the first hint that I found that wireless CarPlay could be added to the CX-9 by swapping the CMU (and potentially GPS cable and antenna). Some users have done it successfully on Miata's. What you would need is either a Canadian CX-9 2021 CMU or a mazda 6 or Miata CMU. It is way more expensive than a dongle however.
See this thread: ND Club 2021 Wireless Carplay Conversion
See this thread: ND Club 2021 Wireless Carplay Conversion