BindingHelper.cs

using Android.Content;
using Android.OS;
using Android.Util;

public class BinderX<TService, TActivity> : Binder
    where TService : Service where TActivity : Activity
{
    public BinderX(TService service)
    {
        Service = service;
    }

    public TService Service { get; }
    public ServiceConnectionX<TActivity, TService>? ServiceConnection { get; set; }
    public TActivity? Activity => ServiceConnection?.Activity;
}

public class ServiceConnectionX<TActivity, TService> : Java.Lang.Object, IServiceConnection
    where TActivity : Activity where TService : Service
{
    public ServiceConnectionX(TActivity activity)
    {
        Activity = activity;
    }

    public TActivity Activity { get; }
    public BinderX<TService, TActivity>? Binder { get; set; }
    public TService? Service => Binder?.Service;

    public event EventHandler? Connected;
    public event EventHandler? Disconnected;

    public void OnServiceConnected(ComponentName? name, IBinder? service)
    {
        Binder = service as BinderX<TService, TActivity>;
        Binder.ServiceConnection = this;
        Log.Info(GetType().Name, $"OnServiceConnected {name?.ClassName}");
        Connected?.Invoke(this, EventArgs.Empty);
    }

    public void OnServiceDisconnected(ComponentName? name)
    {
        Binder.ServiceConnection = null;
        Binder = null;
        Log.Info(GetType().Name, $"OnServiceDisconnected {name?.ClassName}");
        Disconnected?.Invoke(this, EventArgs.Empty);
    }
}

MainActivity.cs

using Android.Content;

namespace AndroidApp1
{
    [Activity(Label = "@string/app_name", MainLauncher = true)]
    public class MainActivity : Activity
    {
        ServiceConnectionX<MainActivity, MyService> connection;

        protected override void OnCreate(Bundle? savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            SetContentView(Resource.Layout.activity_main);

            connection = new(this);
            Intent intent = new(this, typeof(MyService));
            BindService(intent, connection, Bind.AutoCreate);
        }

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

            UnbindService(connection);
        }
    }
}

MyService.cs

using Android.Content;
using Android.OS;

namespace AndroidApp1
{
    [Service]
    public class MyService : Service
    {
        BinderX<MyService, MainActivity> binder;

        public override void OnCreate()
        {
            base.OnCreate();

            binder = new(this);
        }

        public override IBinder OnBind(Intent? intent)
        {
            return binder;
        }
    }
}