Bear in mind this is a prerelease app on TestFlight and that Apple would not allow this behavior on the App Store, or even on apps notarized for alternative stores in the EU:

> 2.5.9 Apps that alter or disable the functions of standard switches, such as the Volume Up/Down and Ring/Silent switches, or other native user interface elements or behaviors will be rejected.

Infamously, there was a third party camera app, Camera+, that turned the Volume Up button into a shutter release. Apple pulled it from the store—and then released the same feature for the built in Camera app.

https://forums.appleinsider.com/discussion/112111/popular-ip...