Use double tap to perform common actions on Apple Watch Ultra
Use double tap (Apple Watch Ultra 2 only)
On Apple Watch Ultra 2, tap your index finger and thumb together twice to answer a call, reply to a message, see and scroll through your Smart Stack, and more. When you use a double tap, appears at the top of the display. If you use the double tap gesture and it’s not available for a particular screen, shakes from side to side.
You can choose what a double tap does when playing media or navigating your Smart Stack.
Open the Settings app on your Apple Watch Ultra.
Tap Gestures, tap Double Tap, then choose from among these options:
Playback: Choose Play/Pause or Skip.
Smart Stack: Choose Advance or Select.
Turn off Double Tap if you don’t want to use the gesture on your Apple Watch Ultra 2.
You can also open the Apple Watch app on your iPhone, tap My Watch, go to Settings > Gestures, then tap Double Tap.
Note: The double tap gesture isn’t available when Low Power Mode is on, Sleep Focus is active, the display is inactive because your wrist is down, or certain accessibility features are on. Additionally, double tap isn’t available on an Apple Watch you set up for a family member, and works only when your Apple Watch Ultra is on your wrist and unlocked.
See this Apple Support article for more information.