Android 5 is too old - I believe you need 7 and up for this.
The Android app has JavaScript ported from the web app,
using Capacitor
.. which requires at least Android version 7.0 on API 24 to use the Android Emulator.
That web page goes on to suggest that "Physical devices should work
as low as Android 5.0 (API 21) as long as their System WebView is updated."
User comments for the update app are discouraging:
.. and anyway my newest Android device is only 4.2.2 (API 17)
and despite its USB OTG working with some other USB devices,
all six serial terminal Android apps tested hung the nanoVNA.
Oristo