Create a field with SfTextInputLayout that opens SfPopup when tapped

    <Grid Margin="10,50,10,10">
                    <inputLayout:SfTextInputLayout
                        x:Name="birthdayLayout"
                        ContainerType="Outlined"
                        HelperText="Enter your date of birth"
                        Hint="Birth date"
                        LeadingViewPosition="Outside"
                        TrailingViewPosition="Inside">

                        <Entry x:Name="dateOfBirth" Text="{Binding MonthName, Mode=TwoWay}" />

                        <inputLayout:SfTextInputLayout.TrailingView>
                            <Label
                                FontSize="18"
                                Text="D"
                                VerticalTextAlignment="Center">

                                <Label.GestureRecognizers>
                                    <TapGestureRecognizer x:Name="labelGesture" Tapped="GestureRecognizer_Tapped" />
                                </Label.GestureRecognizers>

                                <Label.FontFamily>
                                    <OnPlatform x:TypeArguments="x:String">
                                        <On Platform="iOS" Value="InputLayoutIcons" />
                                        <On Platform="Android" Value="InputLayoutIcons.ttf#InputLayoutIcons" />
                                        <On Platform="UWP" Value="/Assets/Fonts/InputLayoutIcons.ttf#InputLayoutIcons" />
                                    </OnPlatform>
                                </Label.FontFamily>
                            </Label>
                        </inputLayout:SfTextInputLayout.TrailingView>
                    </inputLayout:SfTextInputLayout>

                    <sfPopup:SfPopupLayout IsVisible="false" x:Name="popupLayout">
                        <sfPopup:SfPopupLayout.PopupView>
                        <sfPopup:PopupView HeightRequest="230"
                           HeaderTitle="Month List"
                           ShowFooter="False">
                                <sfPopup:PopupView.ContentTemplate>
                                    <DataTemplate>
                                        <StackLayout x:Name="mainLayout">
                                            <ListView ItemsSource="{Binding NamesList}" ItemSelected="Handle_ItemSelected">
                                                <ListView.ItemTemplate>
                                                    <DataTemplate>
                                                        <ViewCell>
                                                            <Label Text="{Binding Name, Mode=TwoWay}" />
                                                        </ViewCell>
                                                    </DataTemplate>
                                                </ListView.ItemTemplate>
                                            </ListView>
                                        </StackLayout>
                                    </DataTemplate>
                                </sfPopup:PopupView.ContentTemplate>
                            </sfPopup:PopupView>
                        </sfPopup:SfPopupLayout.PopupView>
                    </sfPopup:SfPopupLayout>
                </Grid>

  private void GestureRecognizer_Tapped(object sender, System.EventArgs e)
  {
            popupLayout.IsOpen = true;
            popupLayout.Focus();
  }

  void Handle_ItemSelected(object sender, Xamarin.Forms.SelectedItemChangedEventArgs e)
  {
            viewModel.MonthName = (e.SelectedItem as Model).Name;
            popupLayout.IsOpen = false; 

   }

 public class ViewModel : INotifyPropertyChanged
 {
        public ObservableCollection<Model> NamesList { get; set; }

        public event PropertyChangedEventHandler PropertyChanged;

        private string monthName;

        public string MonthName
        {
            get { return monthName; }
            set
            {
                monthName = value;
                NotifyPropertyChanged();
            }
        }

        public ViewModel()
        {
            NamesList = new ObservableCollection<Model>()
            {
               new Model(){ Name = "January" },
                new Model(){ Name = "February" },
                 new Model(){ Name = "March" },
                  new Model(){ Name = "April" },
                   new Model(){ Name = "May" },
            }; 
  }

  private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
  {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
   }

    public class Model: INotifyPropertyChanged
    {
        private string name;

        public string Name
        {
            get { return name; }
            set
            {
                name = value;
                NotifyPropertyChanged();
            } 
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }