UIAccessibility notifications not being posted by UIKit

Code:

override func viewDidLoad() {
    ...
    NotificationCenter.default.addObserver(self, selector: 
#selector(closedCaptioningStatusChanged(_:)), name: 
.UIAccessibilityClosedCaptioningStatusDidChange, object: nil)
}

@objc func closedCaptioningStatusChanged(_ notif: NSNotification) {
    print("closedCaptioningStatusChanged")
}

I tried changing CC settings in accessibilities and in the default video player. Any ideas why closedCaptioningStatusChanged is not called?
EDIT:
Notifications for all UIAccessibility settings are not called for some reason. Is there something I'm not doing?


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