As mentioned previously you can set a fixed height and width. However you should not put the pixel size in the fields, but the Point size. Without it you do not take the scale factor into account. for instance:
// iPhone X - Px res: 1125 x 2436 - Scale factor: 3.0
#if DEBUG
struct ContentView_Previews : PreviewProvider {
		static var previews: some View {
				return ContentView().previewLayout(.fixed(width: 2436 / 3.0, height: 1125 / 3.0))
		}
}
#endif
`
After some tests, it looks like you have to use the UIKit Scale Factor and not the Native Scale factor for better preview rendering
Link - https://developer.apple.com/library/archive/documentation/DeviceInformation/Reference/iOSDeviceCompatibility/Displays/Displays.html to sizes and scale factor
Topic:
App & System Services
SubTopic:
Core OS
Tags: