Swift 5 @unknown case. Compiler bug ?

I have adapted code to Swift 5. No issues, no correction to make, compatibility is great.

However, I have a switch case for AVCaptureDevice.authorizationStatus:

        switch AVCaptureDevice.authorizationStatus(for: .video) {
        case .authorized:  accessGranted = true
  
        case .notDetermined:  AVCaptureDevice.requestAccess(for: .video) { granted in
                if granted { accessGranted = true  }
            }
        case .denied:
            return
        case .restricted:
            return
        }

I get a (logical) warning: Handle unknown values using "@unknown default"

I am proposed a fix (not always: in a second code, with the exact same sequence, on the same machine, same Switch5 setting, I don't get the fix proposed) to add at the end

@unknown default:

<#fatalError()#>

I accept and implement this:

        case .restricted:
            return
           @unknown default:
           return
       }

Then error at line 2: Expected expression in 'return' statement

If I add a semi colon after return

        case .restricted: // The user can't grant access due to restrictions.
            return;
        @unknown default:
            return
        }

Everything OK, and identation correct.

@unknown is interpretated as the argument for return

Is this a known bug ? Or expected behavior ?