App+Web has re-imagined the concept of engagement. Instead of having sessions and bounce rate, they record engaged sessions and engagement rate.
Engaged sessions are “sessions that lasted longer than 10 seconds, or had a conversion event or 2 or more screen views.”
Engagement rate is Engaged sessions / Sessions.
Therefore, if you really want to see a somewhat equivalent metric to bounce rate, subtract your engagement rate by 1.
More information on App+Web metrics can be found here.