watchOS

Apple Watch is designed to keep information flowing from your iPhone to your wrist. The convenience of not looking at your phone is sometimes replaced by a barrage of notifications on the watch. Apps are set by default to "mirror iPhone alerts", which means any notifications appearing on the iPhone are delivered to Apple Watch. If you find that too many alerts are popping up, watchOS notifications can be customized or disabled.

Apple Watch owners having firmware problems can now try recovering their wearable device directly from an iPhone. This wireless method, while not foolproof, can avoid a trip to Apple for service. If your Apple Watch freezes up, crashes during the update process, or stops working, it may prompt you to initiate a restore. To use this feature, the iPhone requires iOS 15.4 or later and the Apple Watch must be running watchOS 8.5 or later.

According to Apple Support:

Selling or trading in a used Apple Watch? The best way to protect personal data before handing over your old device is to factory reset. Following this procedure wipes the Apple Watch clean, leaving it set up with the default configuration found new in the box. Apple Watch data is largely backed up on iCloud and via the paired iPhone, so owners can transfer this information to a new watch.