I’m not paranoid, but sometimes you can get in such situations in life or interact with such people/community that you could appreciate some extra steps of privacy protection even inside/on your phone. So a few of my ideas for this app with a lot of sensitive personal data stored in it (even if it’s only on the device itself or in iCloud):
A small detail, but I would automatically hide the content/screen of the app in the multitask view, where it shows you the screen of the app for a while after switching to another app. So that it doesn’t show up a map and timeline of your day for example outside the app in the multitask view.
The previous idea kind of stems from the following idea: an optional app lock feature would be also useful, so that you have to authenticate with FaceID or TouchID before being able to access the content of the app. Of course with an app lock you would hide the app screen in the multitask view too by default after leaving/locking the app similarly to banking/messaging apps with extra security/privacy features.
Another idea is just a suggestion to maybe have more security/privacy options for backups (or maybe even exports) like password protected/compressed/encrypted etc. backups or choosing different backup/exports file location (like alternative cloud services, or maybe on device local/offline).
Probably my best inspiration for privacy features for a mobile app would be banking apps and messaging apps or password manager/authenticator apps, especially apps/services with end-to-end encryption. I’m not a security expert so I don’t know if there are ways to improve the security of the internet communication/server side things of the app for example but just another thing that maybe worth mentioning regarding this topic.
Not sure if they good ideas or that many users would find them useful, it’s just something I personally have been thinking about more recently in general. 