Using protobuf generated classes in an UWP app fails

I have trouble using generated classes in my UWP app. The Xaml compile gives me an error message when I try to compile my solution:

Xaml Internal Error error WMC9999: Cannot determine the item type of collection type 'Google.Protobuf.Collections.RepeatedField`1[System.String]' because it has more than one Add method or ICollection implementation. To make this collection type usable in XAML, add a public Add(object) method, implement System.Collections.IList or a single System.Collections.Generic.ICollection.

My protobuf looks like this:

syntax = "proto3";
option csharp_namespace = "MyNamespace";
package basics;

message TestClass{
    string TestProp       = 1;
    repeated string Names = 2;
}

I used these nugets to generate the class:

<PackageReference Include="Google.Protobuf" Version="3.17.3" />
<PackageReference Include="Grpc.Tools" Version="2.40.0"/>

To produce the error is quite easy. Just put an ObservableCollection or List of Type 'TestClass' into the code behind of a Page:

public sealed partial class MainPage : Page
{
    public List<TestClass> TestClasses { get; } = new List<TestClass>(); // <- this causes the error!

    public MainPage()
    {
        this.InitializeComponent();
    }
}

My questions:

• Is there a way to get rid of this error or compile the protobuf file without getting RepeatedFields?
• What would be a good workflow to use protobuf and grpc in an UWP app? (Apparently mine isn`t)