Which Apple Watch is compatible with iPhone 7?
Which iwatch series is compatible with iPhone 7plus iOS 15.4?
[Re-Titled by Moderator]
iPhone 7 Plus, iOS 15
You can use any apple watch with your iPhone 7 plus as it has the latest update of iOS.
Any current models of apple watch will work, and older Apple watches will work with newer versions of iOS
Set up your Apple Watch - Apple Support