Android: BackButton on Android 16 not working after command from FlyOutPage

[3sRykaert]

Description

After browsing to a page by a command on the FlyoutPage, the back button ain't working anymore.
This only happens on Android 16 (API 36) and does NOT occur on Android 14 (API 34) so it might have something to do with: predictive-back-gesture https://developer.android.com/guide/navigation/custom-back/predictive-back-gesture#update-custom

OK by using Button on DetailPage	NOT OK by using Button on FlyOutPage

Steps to Reproduce

OK Scenario:

1. Open the sample app from https://github.com/3sRykaert/MauiMemoryleak/tree/BackButtonNotWorking
2. Click the button to go to the "DetailPage1" on "StartPage"
3. Press the Android Back Button
4. A PopUp appears to show you have pressed the BackButton (which is ok)
5. Click the button to go to the "StartPage" on "DetailPage1"
6. Click the button to go to the "DetailPage1" on "StartPage" (same as step 2)
7. Press the Android Back Button (same as step 3)
8. A PopUp appears to show you have pressed the BackButton (which is ok)

NOT OK Scenario

1. Open the sample app from https://github.com/3sRykaert/MauiMemoryleak/tree/BackButtonNotWorking
2. Click the button to go to the "DetailPage1" on "StartPage"
3. Press the Android Back Button
4. A PopUp appears to show you have pressed the BackButton (which is ok)
5. Open the "FlyOut Page" and there press the button to go the "StartPage"
6. Click the button to go to the "DetailPage1" on "StartPage" (same as step 2)
7. Press the Android Back Button (same as step 3)
8. NO PopUp appears to show you have pressed the BackButton (which is not ok) (also breakpoint in protected override bool OnBackButtonPressed() on MasterPage.xaml.cs does not hit)

Link to public reproduction project repository

https://github.com/3sRykaert/MauiMemoryleak/tree/BackButtonNotWorking (so repo: https://github.com/3sRykaert/MauiMemoryleak/ but branch BackButtonNotWorking)

Version with bug

10.0.20

Is this a regression from previous behavior?

Yes, this used to work in Xamarin.Forms

Last version that worked well

Unknown/Other

Affected platforms

Android

Affected platform versions

Only tested on Android (14 is not impacted, 16 is)

Did you find any workaround?

No

Relevant log output

[TamilarasanSF4853]

This issue has been validated in Visual Studio Code 1.108.0 with MAUI versions 10.0.10, 10.0.11, and 10.0.20. It is reproducible from version 10.0.11 on the Android 16 platform.
In MAUI versions below 10.0.11, clicking the close button closes the app, so the issue could not be verified in those versions.
Note: The issue was not reproduced on Android 14.

Android.14.10.0.20.mov

Android.16.10.0.20.mov

[3sRykaert]

some extra info:
when i add android:enableOnBackInvokedCallback="false" in the application tag in the AndroidManifest.xml it works as expected but this is just a temporary opt-out solution, see: https://developer.android.com/guide/navigation/custom-back/predictive-back-gesture#opt-out
Changing the MainActivity.cs to EnableOnBackInvokedCallback = false as described here: #32458 (comment) doesn't solve it. Shouldn't this change have the same effect as changing the AndroidManifest.xml file?
I have also used the Maui source itself (with the Maui.Controls.Sample.Sandbox project) to try to submit a pullrequest to fix the issue, but the PredictiveBackCallback.OnBackInvoked in MauiAppCompatActivity doesn't even "hit" in the above scenario.
Does this mean it's a bug in Android itself instead of in Maui?

[Sztub]

I ran into same issue after upgrading to .NET 10 on Android 16 but i'm using shell navigation and originally I had two separate Shells — LoginShell and MainShell.

After logging in, I was switching shells by doing:

Shell.Current.Window[0].Page = new MainShell();

At first everything seemed fine, and the back button worked. But after navigating around a bit, it completely stopped responding.

I decided to refactor the navigation flow and removed the LoginShell entirely. I moved everything into MainShell and switched to navigating with:

Shell.Current.GoToAsync("//Main");

Back button seems to work as intended now.

So my question is: Is setting
Shell.Current.Window[0].Page = new MainShell()
actually a valid approach?
I could swear this was recommended years ago as a way to support multiple flyout menus, and now every AI model keeps suggesting it as a solution — but clearly it caused problems in my case.