The problem likely lies with your iPhone's rear camera, which for some reason isn't displaying a preview in the Camera app when active. There's often not much you can do yourself to fix it.
This checks for commonly occurring issues and ensures any new device or hardware is correctly installed on your computer. You can repair the laptop’s camera just by updating your web camera driver.
If your iPhone's camera is having issues Apple might just fix it — and they'll do it for free. The company launched a service program for the Phone 14 Plus. Apple reported that "the rear camera ...
Here’s how to run the Camera troubleshooter: The Camera troubleshooter will Reset the services for your camera, Reset your camera, Update your camera drivers, Use the default Windows camera ...