We've found some similar issues:

• ShellContent Title doesn't observe changes to bound properties #7453 , similarity score: 83%

If any of the above are duplicates, please consider closing this issue out and adding additional context in the original issue.

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I want to confirm with you: I see that your repro step is not consistent with the project content you provided, and I did not use your project to repro your issue. Could you help confirm whether the project you provided is correct?

I want to confirm with you: I see that your repro step is not consistent with the project content you provided, and I did not use your project to repro your issue. Could you help confirm whether the project you provided is correct?

Hi @Ying-6 ,
Yes, I have provided the correct sample. Even if it contains any issues, please use this project for reproducing the issue.
ShellContentTitleIssue.zip

This issue has been verified using Visual Studio 17.13 Preview 1 and VSCode (9.0.10 & 9.0.0 & 8.0.100). Not repro this issue on iOS and MacOS platform.

@Ying-6 ,
The ContentPage title is not set for the ShellContent, causing the ShellContent title to appear in both places. However, if we set the ContentPage title, the ShellContent title does not update at runtime. This behavior is working correctly on the Android platform.

Use this code in AppShell.xaml,

<TabBar AutomationId="TabBar">
        <Tab Title="Nested Tabs" AutomationId="tabbar">
            <ShellContent x:Name="tab"  Title="Hello">
                <ContentPage Title="TabView">
                    <StackLayout HorizontalOptions="Center" Spacing="30">
                        <HorizontalStackLayout>
                            <Label Text="Current Shell Title : " FontAttributes="Bold"/>
                            <Label Text="{Binding Source={x:Reference tab}, Path=Title}" AutomationId="LabelId" />
                        </HorizontalStackLayout>
                        <Button Text="Change Title" AutomationId="ChangeShellContentTitle" VerticalOptions="Center" HorizontalOptions="Center" WidthRequest="100" HeightRequest="40" Clicked="OnButtonClicked"/>
                    </StackLayout>
                </ContentPage>
            </ShellContent>

            <ShellContent Title="Settings">
                <ContentPage Title="TabView" >
                    <Label Text="This is Settings page"/>
                </ContentPage>
            </ShellContent>
        </Tab>
    </TabBar>

Android Behavior(should be expected in iOS)

This issue has been verified using Visual Studio 17.13 Preview 1 and VSCode (9.0.10 & 9.0.0 & 8.0.100). With the detailed information provided by the user, can repro this issue on iOS and macOS platforms.