I have an app that uses Storyboard (not SwiftUI). Is there a way to define that a particular WKInterfaceButton should receive the "sent action" (as if the user tapped the button on screen) when the user uses the double-tap gesture with their fingers?
If I’m understanding correctly, you want to use the Double Tap gesture that’s available on Apple Watch Series 9 and later and Apple Watch Ultra 2. It is not possible to use the Double Tap gesture with storyboards, which were deprecated as of watchOS 7. The .handGestureShortcut modifier is SwiftUI API only.
https://developer.apple.com/documentation/watchos-apps/enabling-double-tap/