To make a React Native app portrait only, we change our app’s manifest.xml.
For instance, we write
<activity
android:name=".MainActivity"
android:configChanges="orientation"
android:screenOrientation="portrait"
>
...
</activity>
to set android:configChanges
to orientation
to change the orientation of our app.
And we set android:screenOrientation
to portrait
to keep the app in portrait mode.