MauiProgram.cs

using Microsoft.Extensions.Logging;
using Microsoft.Maui.LifecycleEvents;
using Plugin.Firebase.Analytics;
#if ANDROID
using Plugin.Firebase.Core.Platforms.Android;
#elif IOS
using Plugin.Firebase.Core.Platforms.iOS;
#endif

namespace GoogleAnalyticsMAUISample
{
    public static class MauiProgram
    {
        public static MauiApp CreateMauiApp()
        {
            var builder = MauiApp.CreateBuilder();
            builder
                .UseMauiApp<App>()
                .RegisterFirebaseServices()
                .ConfigureFonts(fonts =>
                {
                    fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
                    fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
                });

#if DEBUG
    		builder.Logging.AddDebug();
#endif


            return builder.Build();
        }
        private static MauiAppBuilder RegisterFirebaseServices(this MauiAppBuilder builder)
        {
            builder.ConfigureLifecycleEvents(events => {
#if IOS
                events.AddiOS(iOS => iOS.WillFinishLaunching((_, __) => {
                    CrossFirebase.Initialize();
               
                    return false;
                }));
#elif ANDROID
                events.AddAndroid(android => android.OnCreate((activity, _) =>
                {
                    CrossFirebase.Initialize(activity);
                    FirebaseAnalyticsImplementation.Initialize(activity);
                }));
      
#endif
            });

            return builder;
        }
    }
}