I am new in the wonderful world of Xamarin. Yesterday, I Install Xamarin on my VS2017 and on my Mac Mini installed no ElCapitan (10.11.3). Then I compile the basic template "Welcome to xamarin forms". Selecting IphoneSimulator I got several simulator available (Iphone, Ipad, ...) But when running the code I got an error asking me to upgrade XCode to version 8.3 min (Avalaible only with Sierra OS).
So today I reinstall the Mac mini with Sierra (10.12.6) then reinstall Xamarin and XCode 9. I reconnect the Mac Agent in VS2017 and all working but now I do not have any simulator in the IOS project. I select: Debug->IphoneSimulator->App1.iOS and the only choice are Simulator and Device. When I select Simulator and run the project, I got this error: "Please select a valid device before running the application."