AREnvProbe had Desktop Renderer and Metal v.2.1 enabled
See https://issues.unrealengine.com/issue/UE-81660 for fix
If Metal Desktop Renderer and Metal v2.1 are both active, the AR passthrough camera renders as black.
Issue not observed if only 'Metal Desktop Renderer' or 'Metal 2.1' is selected
Issue not observed in 4.23.1
4.25 MAIN (11104400) verification blocked by unresponsive editor on 'launch on' [Link Removed]
Result: View will be black (UI will still be visible) - Some visibility can be gained by placing finger over camera
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-87468 in the post.