When publishing to iPhone I very often get this message: similar detritus not allowed

Code signing no longer allows any file in an app bundle to have an extended attribute containing a resource fork or Finder info.

To see which files are causing this error, run this command in Terminal:

$ xattr -lr <path_to_app_bundle>

replacing with the path to your actual app bundle.

And you can also remove all extended attributes from your app bundle with the xattr command:

$ xattr -cr <path_to_app_bundle>

For more information click here.

Seems it does not have to be necessarily related to Xamarin but rather to signing of application and so to iOS development itself. You could try already existing solutions for code signing issues in

Code Sign Error in macOS High Sierra Xcode - resource fork, Finder information, or similar detritus not allowed

or

Code Sign Error on macOS Sierra, Xcode 8

Hope it could help you.