Mirror your workouts on Apple Watch to your paired iPhone.
Please use it for workouts such as treadmill or cycling that you can do while looking at your iPhone.
While mirroring, Live Activities is displayed.
Swipe to delete.
Live activities have a limited display time. iOS will automatically end the live activities after 8 hours.
Reference: Displaying live data with Live Activities > Understand constraints
To view live activity again, stop and start the mirror.