It should theoretically be possible to hard reset an Android phone & never ever connecting it to the internet again.

It should still be able to generate keys and do basic cryptography. Also screen & camera can provide airgap.

Is there any software that does this? Is it too risky because idiots would use it wrong (not cold)?

Or any technical reason that would prevent it? There are so many old unused Android phones lying in drawers worldwide. It could lower the barrier to entry a lot.

Another advantage IMO is that general purpose hardware - instead of specialized Bitcoin hardware where all the suppliers of the supply chain and delivery companies know that it will hold value.