I think a good decoy feature would be to insert a specific pass phrase to not reset the entire device, but to permanently delete specific (pre-specified) folders on the phone such as chat logs, documents, and specific apps.

GrapheneOS wipes the device, and that's apparently enough to get people in trouble in the US. If the phone kept on working as normal without notifying anyone of anything unusual, but deleted sensitive documents behind the scenes, that would be really cool for these types of situations.

I'm not sure fingerprints would be useful for this. You can always just enter a pass phrase instead, and it would be very annoying to trigger it by accident which would almost certainly happen to some people. It would be neat if different fingerprints could be used to load different user profiles.