so ideally you would want some secure enclave like knox (or a second phone) locked with a strong pin. and never unlock that in a public space under cameras. idk how good knox actually is, i keep putting that research off. the idea is that, you in fact unlock the basic functions (or your burner) with biometrics (maybe coupled with an nfc security device attached to your body) but that does not include any truly private data or privacy sensitive apps like e2e messengers or wallets.

Don't make it harder than it is. A privacy screen runs for $10 and graphene and other OSs have option to scramble pin input layout so there is no order to capture. The more difficult it is the less likely you are going to do it.