Do you have the same WebView version on both Android 10 devices? You can check this via the Settings menu on your device, the name will be "Android System WebView" or something similar. If the non-working device is using an older version that might be the reason.
Is this also applicable to the QR decoder?
We are not aware of such limitations. As long as your device is running a recent version of Android WebView, it should be fine.
Is your test project similar to the code your posted earlier or did you modify it?