Latest Android release has some protection for this now – no idea how good it is but probs better than nothing.
it’s a good idea generally but just a red-herring in this instance. No-one is getting access to your bank accounts just because they have your unlocked phone and nothing else.
The 2 scenarios I’ve read about involving money actually being taken via a stolen phone have been 1) mugged and then PIN/password etc extracted at knifepoint (not much you can do about that!!), 2) thief observes you entering PIN carelessly and then steals phone (on an iPhone this would just give access to Wallet for contactless payments rather than banking apps, etc)