How to sync notes from iPhone 6 to iPhone 7?

Through icloud: Settings - icloud, turn on the switch of "Memories". If it was turned on before, it means it has been turned on. If it was just turned on, click "Storage and Backup" below. , click the Backup Now button at the bottom until the backup is completed. Then turn on this switch on the new phone as well, then connect the phone to wifi, connect to the power source for charging, and lock the screen. The iPhone will automatically download the backup.

Backup and restore through third-party tools: For example, use itools, connect your phone to the computer, open itools, there is an information management tab on the left column, click it and find the memo tab on the right, go in and back up the memo, and then Connect the iPhone to the computer, and import the previously backed up notes here.