Does anyone know why my SiriusXM app disappeared off my iPhone Home Screen? It shows it open in the App Store.

With iOS 14, apps can be removed from the home screen without being deleted.. If you have iOS 14, go to the App Library (swipe left past your last home screen). From there you can touch and hold an app and slide it left back to the home screen.

Hard to say, it could have accidentally been deleted. Just go back to the App Library, find the App, press and hold and drag it back to a home screen.