can't use FileOpenPicker in uwp c# .net core, any alternative ways to upload pictures in uwp?

I wan't to create a photo uploading method for my uwp app but there is no way to do it because I can't use FileOpenPicker or any of the other pickers! It cannot find FileOpenPicker, even if declared like Windows.Storage.Pickers.FileOpenPicker(); It complains about the type or namespace Windows not being found. Even when I put using Windows.Storage.Pickers; at the top of the file I have installed NuGet UwpDesktop-Updated to no avail. This is strange because I have been googling for days without finding anyone else with my issue!

Are there any other ways to upload a photo in uwp with c# .net core?

using System;
using System.Windows.Controls;
using Image.ViewModels;
namespace Image.Views
{
    public partial class MainPage : Page
    {
        public MainPage(MainViewModel viewModel)
        {
            InitializeComponent();
            DataContext = viewModel;
        }

        private async void Clicked(object sender, EventArgs e)
        {
            var picker = new Windows.Storage.Pickers.FileOpenPicker();
            picker.ViewMode = Windows.Storage.Pickers.PickerViewMode.Thumbnail;
            picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.PicturesLibrary;
            picker.FileTypeFilter.Add(".jpg");
            picker.FileTypeFilter.Add(".jpeg");
            picker.FileTypeFilter.Add(".png");

            Windows.Storage.StorageFile file = await picker.PickSingleFileAsync();
            if (file != null)
            {
                // Application now has read/write access to the picked file
                this.textBlock.Text = "Picked photo: " + file.Name;
            }
            else
            {
                this.textBlock.Text = "Operation cancelled.";
            }
        }
    }
}