When Sleep Mode is enabled, the lockscreen will dim, calls and alerts that arrive while locked will be silenced, and notifications will be sent to history. Emergency alerts will break through. Sleep will analyze your sleep patterns based on your iPhone usage at night.
Bedtime in the Clock app can set an alarm and track your time in bed. Do Not Disturb can silence calls and alerts. So if this rumor is true then it sounds Apple is rebranding and combining these disparate features into one Sleep Mode toggle.
Check It Out: New Feature ‘Sleep Mode’ Could Arrive on iOS 14