As far as what is feasible, Apple does a very good job with their iPhone/iPad security. With both hardware and software. You can read about it how it all works

As far as what is feasible, Apple does a very good job with their iPhone/iPad security. With both hardware and software. You can read about it how it all works in their platform security guide. On the Android side, Google makes good software changes to Android, but ultimately the security is dependent on the handset maker (e.g. Samsung) and SoC maker (e.g. Qualcomm). Security will vary between Android phones. The bigger Android phone makers are more able to make security investments than the cheaper phone makers.