May I know if you have a chance to check my answer ? If you still have problem please let me know.

Kindly take a look at UIDocumentPickerViewController , from iOS13 it allows to select folder with setting the content type to folder. And another way is to use Xamarin.Essentials FilePicker, you can try the method in the link .

Have you tried Xamarin.Essentials FilePicker I mentioned ? It seems to support selecting directory.

You could define the type like "application/comics" , check https://docs.microsoft.com/en-us/xamarin/essentials/file-picker?tabs=android#pick-file .

Consider raising this issue on github for better support : https://github.com/xamarin/Essentials/issues.

Gerald Versluis explained in the comment the event handlers are not used to avoid the app from crash , they're a last resort to give you an opportunity to do something like writing to an error log before the application is terminated . Refer to the docs : https://docs.microsoft.com/en-us/dotnet/api/system.appdomain.unhandledexception?redirectedfrom=MSDN&view=net-6.0#remarks . Actually, this is by design, the OS crashes your app and let you know what's going wrong rather than keep running with something unexpected happens.

For how to integrate FCM on Xamarin.iOS , refer to the tutorial in this link : https://github.com/xamarin/GoogleApisForiOSComponents/blob/main/docs/Firebase/CloudMessaging/GettingStarted.md .

It seems the problem has been solved here : https://stackoverflow.com/questions/70963556/error-compiling-xamarin-application-on-release-mode-system-invalidoperationexce.

Did you test on Android or iOS ?

First download Visual Studio for mac , then you can develop your C# project now.

Can you provide the complete code (viewmodel) ? If you want to enable group ,the viewmodel should look like here : https://docs.microsoft.com/en-us/xamarin/xamarin-forms/user-interface/collectionview/grouping#example .

Well , it looks like a potential issue , consider raising the issue on github here :https://github.com/xamarin/xamarin-macios/issues

You can add breakpoint to debug which line calls first .

In your comment Line14 calls first than Line 11, so RecivedSelectedNotebook is null .

@YoungCalabria-7310 , I'm testing on Android simulator but it works fine , toolbar item displays the icon with original color as expected. If possible could you provide a basic, reproducible project here for testing ? You can simply upload it to github and attach the link here .