presence/Presence.Desktop/ViewModels/PresenceViewModel.cs

using System.Reactive;
using ReactiveUI;

namespace Presence.Desktop.ViewModels;

public class PresenceViewModel: ViewModelBase, IRoutableViewModel
{
    public string? UrlPathSegment { get; }
    public IScreen HostScreen { get; }

    public ReactiveCommand<Unit, Unit> GoBackCommand { get; }

    public PresenceViewModel(IScreen hostScreen)
    {
        HostScreen = hostScreen;

        GoBackCommand = ReactiveCommand.Create(() =>
        {
            HostScreen.Router.Navigate.Execute(new StartViewModel(HostScreen));
        });
    }
}