Getting smooth waypoint flights with my DJI Air 2

That’s not entirely correct, it still uses the SDK.

All Litchi compatible drones that use the DJI Fly app are controlled using VSC (Virtual Stick Commands), starting with the Mavic Mini in 2019.
VSC is implemented by DJI in their SDK for these drones.

The Mavic Air(1) is 4k capable.

Have a look at this thread: