Regarding the new ARKit 6 API that takes a 4k photo of the AR scene, is there a limit to how many times it can be called? Can I take say 30 photos within a second?
You can take the next photo right after the completion handler of your previous captureHighResolutionFrame call - or even from within the completion handler.
If you try taking a new photo before the previous call completed, you will receive an ARError.Code.highResolutionFrameCaptureInProgress error in the completion handler/