My screen mirroring has been deleted from my iPhone 11

What do you mean it has been deleted? It's a built in feature of iOS. Do you mean it has been removed from the Control Center?

Edit Control Center on your iPhone, iPad, and iPod touch - Apple Support

Screen mirroring cannot be removed from the phone and cannot be removed from the control center either. However, the icon for it changed to 2 overlapping rectangles.

Again, it's not something that can be removed. Did you look at the article I linked to that tells you how to add and remove things from Control Center? One of those things is screen mirroring.