That is true. Non-cellular iPads do not have GPS so they will not support RTC. That is not a s/w bug in DJI GO 4 app. However, every iPhone does have GPS does not work and that is a bug in GO 4.
Didn't know that about GO 4. I've had GPS in all of my iOS devices ever since I discovered that my non-cellular iPad wouldn't work with my APRS app because it didn't have GPS.
Also - I use DJI Fly, because I'm using a Mavic Air 2.