Picker don't show anything

Hi all togehter,
i have serious problems with the Picker:

    <Picker BackgroundColor="Red"
                      Title="Select Job" 
                      ItemsSource="{Binding Projects}"
                      SelectedItem="{Binding SelectedProject,Mode=TwoWay}"
                      ItemDisplayBinding="{Binding SelectedProject.ProjectId}"                                                      
      ></Picker>

My ViewModel:

Project _selectedProject;
    public Project SelectedProject
    {
        get => _selectedProject;
        set => SetProperty(ref _selectedProject, value);
    }

    ObservableCollection<Project>  _projects;
    ObservableCollection<Project> Projects
    {
        get { return _projects; }
        set { SetProperty(ref _projects, value); }
    }

var items = new ObservableCollection();

var projects = (IEnumerable)parameters["Projects"];

foreach (Project project in projects)
{
items.Add(project);
}
Projects = items;
SelectedProject = Projects.FirstOrDefault();

My PickerControl don't Show anything, no list of items, definitly nothing....

Databinding to other Controls like TableView works, i just remove them for Debugging

Any idea
Peter