If the rhiwindow example is run with --metal option it fails with:

Users/x/Local/Python/PySide6/examples/rhiwindow/rhiwindow.py:179 in init 
  179 self.m_rhi.reset(QRhi.create(QRhi.Implementation.Metal, params))
AttributeError: Error calling Python override of QWindow::exposeEvent(): 'NoneType' object has no
attribute 'reset'

I replaced the failing line with:

  self.m_rhi = QRhi.create(QRhi.Implementation.Metal, params)

and that allowed the example to run without crashing.