No virtual devices found - Ionic Cordova Emulate iOS

Or you could just try something like this :

cd platforms/ios/cordova
npm install ios-sim@latest

If this problem again persist after updating to Mojave then remove and add platform will not going to work.

Instead you can try invoking simulator directly using following command

ionic cordova emulate ios --livereload --consolelogs --target="iPhone-6,com.apple.CoreSimulator.SimRuntime.iOS-12-2"

Also, if you are using older build system, you can add additional flag like below

ionic cordova emulate ios --livereload --consolelogs --target="iPhone-6,com.apple.CoreSimulator.SimRuntime.iOS-12-2" --buildFlag="-UseModernBuildSystem=0"