A solution could be having a tiny non-rooted Android system as a "coprocessor".

This won't work. The tiny non-rooted system wouldn't get certified by Google and therefore not pass hardware attestation, which most banking apps use.

	▲	hyghjiyhu a day ago \| parent \| next [-]
		Well you could take a certified system off-the-shelf and integrate it into a bigger thing.
	▲	NoGravitas a day ago \| parent \| prev [-]
		I think they mean having a second non-rooted phone that is certified but cheap.