accessibilityActivate() lets you capture a VoiceOver double tap. This is useful if you are creating a custom component you interact with using complex gestures or VoiceOver navigation gestures. An example: slide to unlock.

https://developer.apple.com/documentation/objectivec/nsobject-swift.class/accessibilityactivate()

The classic Slide to Unlock component used in iOS for unlocking your device, in the first iOS versions, required sliding a button with an arrow to the right. This clashed with a flick to the right gesture used with VoiceOver to navigate to the next item. It would try to find the next element on screen instead of unlocking the device and it would play a sound indicating you’ve reached the end of the screen. So you could double tap to activate instead. This can be achieved by overriding accessibilityActivate() in the slide to unlock component.