The application is not adapted to new displays, and 2 years have passed...
The app hasn't been updated since a while; users have been complaining about this since the iPhone X came out in 2017: Stack Exchange app iPhone X optimization
However, this issue won't be addressed, as the apps have been abandoned. Quoting a Stack Exchange developer:
We are not providing any further support for the mobile apps. There will not be any more builds made for either the Android or the iOS app (even for breaking bugs). We encourage all mobile users to use the responsive website. We hope to continue to incrementally improve the user experience for mobile users.