I'm sharing this in case someone else wants to use Apple's RoomPlan to create a model and import it into Blender.
The problem: I could not successfully import a USDZ model from the RoomPlan app into Blender. (I went through the normal process of importing a USDZ file into Blender: change the file type from ".usdz" to ".zip"; unzipped the file; then tried to import the ".usda" file). No surfaces appeared.
The solution: In Apple's source code from here, in the file RoomCaptureViewController.swift, I changed the line
try finalResults?.export(to: destinationURL, exportOptions: .parametric)
to
try finalResults?.export(to: destinationURL, exportOptions: .mesh)
recompiled, and went through the USDZ to USDA conversion process again. This time it worked.
Apparently Blender cannot import parametric USDA models.