In iOS 12, Apple refined the way QR scanning works. The operating system now allows you to scan QR code directly from Control Center through a new shortcut. It works even if you have disabled QR scanning from the Camera settings.
Step#1: Open Settings.
Step#2: Swipe down and tap Control Center. Then, tap Customize Controls.
Step#3: Swipe down and tap Scan QR Code to add the shortcut.
Control Center iOS 12
Scan QR Code setting iOS 12
Step#4: Open the Control Center by swiping from top-left on an iPhone or by sliding up on an iPhone 8 or older.
Control Center View
Step#5: Look for the QR code icon.
Step#6: While scanning, notice there is a new yellow highlighting frame.