I have a 12.9" iPad Pro (3rd Generation) which has a USB-C connection, a compatible device according to DJI. When i open the DJI Fly app, it has a message at the top of the screen in red saying "RC not connected to mobile device". Searching on the net and forums i have not yet found a solution to this problem. It works when I'm using my iPhone 11 just not my iPad Pro.
Have tried multiple USB-C cables
Tried "rotating connector 180 degrees" as some suggested
Yes, I'm plugged into the port on the right side in controller, not the dummy port to the left.
Tried plugging power into controller at same time as has been suggested
Checked for firmware updates and nothing new available
Restarted all devices

I'm at a loss as to why this doesn't work, so many have the problem, yet i can't find any solutions.

Need help.

Hello there DarthDazza. I am sorry for the trouble this has caused and thank you for reaching out. Kindly please uninstall and reinstall the DJI Fly application ( https://www.dji.com/downloads/djiapp/dji-fly ) and kindly please try using a different cable if you have an extra one to connect the said DJI Remote Controller to the said mobile device for us to be able to isolate the said issue. In addition, kindly please sync all of your flight records before uninstalling the DJI Fly application on your mobile device for you not to loose your previous flight information. Thank you.

Exact same issue on my side.  Mine is same model and firmware ipad / works with my mini but not new 2s. / cables, cables, cables tried them all / delete and reload / power on-of. I think its an apple thing / usb-c

This is the third post I have seen about the iPad12.9 not working with the FLY.  The iPad 12.9 uses iPadOS which was released in September 2021.  Apps for iPadOS have to be configured slightly differently than IOS.  The problem may be an issue with iPadOS or that the DJI FLY apps compatibility with iPadOS.  But given that other DJI drones like the Mavic Mini and Air 2S do not work with the iPad it is more than likely a DJI issue.