The problem

Neither the iOS Simulator nor the Android Emulator has real camera hardware. If you're building anything that touches AVCaptureSession — a QR scanner, a document capture flow, an AR feature — you end up with one of two workflows:

Test exclusively on a physical device, every time, for every camera-touching change

Stare at a blank/simulated camera feed in the Simulator and hope for the best

Neither is great when you're iterating quickly.