Double swiping from bottom not supported in iOS 15?

Since the iPhone X, you will not be able to block the home gesture via preferredScreenEdgesDeferringSystemGestures. This property is only effective on iPhones without home buttons that allow the invocation of the control center via a swipe from the bottom of the screen.

Could you explain what you're trying to accomplish exactly? Perhaps what you really want is prefersHomeIndicatorAutoHidden. This setting will automatically hide the home indicator after some time while your view controller is presented, and the user will have to swipe up twice in order to go home. This allows your app one chance to respond to a gesture from the bottom of the screen (but only one).

// Controls the application's preferred home indicator auto-hiding when this view controller is shown.
@property (nonatomic, readonly) BOOL prefersHomeIndicatorAutoHidden API_AVAILABLE(ios(11.0)) API_UNAVAILABLE(watchos, tvos);