Unable to find application Mono.Android.Platform.ApiLevel_24 or Xamarin.Android.Platform

Disabling Use Shared Runtime from Project ->Options->Android Options solved it.

Yes as mentioned in the answer above:

Disabling Use Shared Runtime from Project -> Options -> Android Options 

should work in most cases, and that is indeed the first thing to try. But if that doesn't work, you may also try to add to the list of supported architectures from Android Project Properties -> Advanced as shown in the images below.

Hope this helps.