您可以尝试将Reference设置为DatePicker，并将path设置为Date。
请参考以下代码：

<DatePicker x:Name="mDatePicker"   MinimumDate="01/01/2020" MaximumDate="12/31/2022" Date="01/01/2022" DateSelected="DatePicker_DateSelected" /> 

        <Entry Placeholder="text" Text="{Binding Source={x:Reference mDatePicker}, Path=Date }"   />

注：

如果使用TimePicker，则可以将Path设置为Time

<TimePicker x:Name="timePicker" />
    <Label Text="{Binding Source={x:Reference timePicker},
                          Path=Time,
                          StringFormat='The TimeSpan is {0:c}'}" />

更新日期：

从你发布的新帖子中，我发现你想把你的DesktopStartupPage.xaml.cs中定义的变量time1绑定到一个Entry上，如下所示：

public DateTime time1 { get; set; }

<Entry Placeholder="text" Text="{Binding Source={Binding time1},
                              Path=Time,
                              StringFormat='The TimeSpan is {0}'}" Style="{StaticResource tableContStyle}" Grid.Row="1" Grid.Column="0"

/〉
然后我们需要直接绑定变量，如果你想在改变变量的值后更新UI，你可以为你的页面实现接口INotifyPropertyChanged。
请参考以下代码：

主页.xaml

<?xml version="1.0" encoding="utf-8" ?> 
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiScrollApp1212.MainPage">

    <ScrollView>
        <VerticalStackLayout
            Spacing="25"
            Padding="10"
            VerticalOptions="Center">

            <DatePicker x:Name="mDatePicker"   MinimumDate="01/01/2020" MaximumDate="12/31/2022" Date="01/01/2022" DateSelected="DatePicker_DateSelected" />

            <Entry Placeholder="text" Text="{Binding Source={x:Reference mDatePicker}, Path=Date, StringFormat='The TimeSpan is {0:c}' }"   />

            <Button HeightRequest="60" WidthRequest="300"  x:Name="inbtn" Text="In"   Clicked="OnInClicked" HorizontalOptions="Center" />

            <!--<Entry Placeholder="text" Text="{Binding Source={Binding Time1},  
                              Path=Date,
                              StringFormat='The TimeSpan is {0}'}"  />-->

            <Entry Placeholder="text" Text="{Binding Time1, StringFormat='The TimeSpan is {0}'}"  />


        </VerticalStackLayout>
    </ScrollView>

</ContentPage>

主页面.xaml.cs

public partial class MainPage : ContentPage, INotifyPropertyChanged 
{
    //public DateTime time1 { get; set; }

    DateTime _time1;
    public DateTime Time1
    {
        get => _time1;
        set => SetProperty(ref _time1, value);
    }

    public MainPage()
      {
            InitializeComponent();

        Time1 = DateTime.Now;

        this.BindingContext = this;
    }


    private void DatePicker_DateSelected(object sender, DateChangedEventArgs e)
    {
        Time1 = mDatePicker.Date;
    }
    private void OnInClicked(object sender, EventArgs e)
    {
        //Time1 = DateTime.Now;
        Console.WriteLine(Time1);

       // GetCachedLocation();
    }


    bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
    {
        if (Object.Equals(storage, value))
            return false;

        storage = value;
        OnPropertyChanged(propertyName);
        return true;
    }

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}