You just bought a new iPhone 13. Do you have an old iPhone that you would like to move data from? If YES, then you can click on that notification message and then backup your old iPhone to iCloud and restore your new iPhone from iCloud. This is a free service provided by Apple for those who would like to bring over data from an old iPhone to a new one.
If you have already setup your new iPhone 13 to the way you like it, then ignore that message and it will eventually go away.
Axel F.