My Xamarin project not displaying values in ListView

I'm starting to learn Xamarin. I followed this video course: Youtube Link.

I have an SQLite database populated, that i added (in root) in the code project as embedded resource. If I check ItemPage.xaml, there is a black windows and i don't see any listview. (This is a Master-Detail project with .net standard).

I checked with the debugger, the ExecuteLoadItemsCommand gets the rows from the db, but the listview didn't display it.

ItemsPage.xaml:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:sfgrid="clr-namespace:Syncfusion.SfDataGrid.XForms;assembly=Syncfusion.SfDataGrid.XForms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:SampleBrowser.SfDataGrid;assembly=SampleBrowser.SfDataGrid"
             xmlns:sys="clr-namespace:System;assembly=mscorlib"
             xmlns:local1="clr-namespace:ZilahiReformatusTemeto.Models"
             x:Class="ZilahiReformatusTemeto.Views.ItemsPage"
              Title="{Binding Title}"
             x:Name="BrowseItemsPage">
    <ContentPage.ToolbarItems>
        <ToolbarItem Text="Add" Clicked="AddItem_Clicked">
            <ToolbarItem.Icon>
                <OnPlatform x:TypeArguments="FileImageSource">
                    <On Platform="UWP" Value="add.png"/>
                </OnPlatform>
            </ToolbarItem.Icon>
        </ToolbarItem>
    </ContentPage.ToolbarItems>
    <ContentPage.BindingContext>
        <local1:Sírok x:Name="viewModel" />
    </ContentPage.BindingContext>

    <StackLayout>
        <ListView 
                ItemsSource="{Binding Sírok}"
                VerticalOptions="FillAndExpand"
                HasUnevenRows="true"
                RefreshCommand="{Binding LoadItemsCommand}"
                IsPullToRefreshEnabled="true"
                IsRefreshing="{Binding IsBusy, Mode=OneWay}"
                
                ItemSelected="OnItemSelected">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <ViewCell>
                        <StackLayout >
                            <Label Text="{Binding Parcellaszám}" 
                                LineBreakMode="NoWrap" 
                                Style="{DynamicResource ListItemTextStyle}" 
                                FontSize="16" />
                            <Label Text="{Binding Sírhelyszám}" BindingContext="{Binding Sírhelyszám}"
                                LineBreakMode="NoWrap"
                                Style="{DynamicResource ListItemDetailTextStyle}"
                                FontSize="13" />
                        </StackLayout>
                    </ViewCell>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>
    </StackLayout>
</ContentPage>

ItemsPage.xaml.cs:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;

using ZilahiReformatusTemeto.Models;
using ZilahiReformatusTemeto.Views;
using ZilahiReformatusTemeto.ViewModels;

namespace ZilahiReformatusTemeto.Views
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class ItemsPage : ContentPage
    {
        ItemsViewModel viewModelg;

        public ItemsPage()
        {
            InitializeComponent();

            viewModelg = new ItemsViewModel();
            BindingContext = viewModelg;
        }

        async void OnItemSelected(object sender, SelectedItemChangedEventArgs args)
        {
            var item = (Sírok)args.SelectedItem;
            if (item == null)
                return;

            await Navigation.PushAsync(new ItemDetailPage(new ItemDetailViewModel(item)));

            // Manually deselect item.
            //SfDataGrid.SelectedIndexProperty = -1;
            //ItemsListView.SelectedItem = null;
        }

        async void AddItem_Clicked(object sender, EventArgs e)
        {
            await Navigation.PushModalAsync(new NavigationPage(new NewItemPage()));
        }

        protected override void OnAppearing()
        {
            base.OnAppearing();

            if (viewModelg.Items.Count == 0)
                viewModelg.LoadItemsCommand.Execute(null);
        }
    }
}

Edit - Added - ItemsViewModel:

    using System;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Threading.Tasks;

using Xamarin.Forms;

using ZilahiReformatusTemeto.Models;
using ZilahiReformatusTemeto.Views;

namespace ZilahiReformatusTemeto.ViewModels
{
    public class ItemsViewModel : BaseViewModel
    {
        public ObservableCollection<Sírok> Items { get; set; }
        public Command LoadItemsCommand { get; set; }

        public ItemsViewModel()
        {
            Title = "Browse";
            Items = new ObservableCollection<Sírok>();
            LoadItemsCommand = new Command(async () => await ExecuteLoadItemsCommand());

            MessagingCenter.Subscribe<NewItemPage, Sírok>(this, "AddItem", async (obj, item) =>
            {
                var newItem = item as Sírok;
                Items.Add(newItem);
                await DataStore.AddItemAsync(newItem);
            });
        }

        async Task ExecuteLoadItemsCommand()
        {
            if (IsBusy)
                return;

            IsBusy = true;

            try
            {
                Items.Clear();
                var items = await DataStore.GetItemsAsync(true);
                foreach (Sírok item in items)
                {
                    Items.Add(item);
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex);
            }
            finally
            {
                IsBusy = false;
            }
        }
    }
}

Here is my project that I'm working on : LINK