I have lost a lot of sleep over this (in the past 3 years). I was hooping that Apple would at least be able to export its own .scn Scenes to USDZ without too much problems.
Has anyone been successful in exporting a .scn scene to USDZ from within an app?
I have tried this but to no avail:
Have you taken a look at this:
Batch Converting Apple SCN files into DAE
xcrun scntool --convert fileIn.scn --output fileOut.dae --format dae
Or this:
https://developer.apple.com/forums/thread/104553
They mention a number of ways such as converting to a dae first, and then using the free converter.