Iphone 16 apple watch 10 backup corrupted?

Unpairing and pairing the Apple Watch again has helped other users.

Unpair and erase your Apple Watch - Apple Support

And, to rule out defective data from the backup, set up the watch as a new device after that.

You will only lose your created Watch faces and may have to activate the cards in your Wallet app again.

Do you have Smart Stack and Live Activities enabled?

Did you already try to force restart your iPhone and Apple Watch?

Force restart iPhone - Apple Support

To force restart your watch, press and hold the Digital Crown and the Side button together for about 10sec, until the Apple logo comes back again.

Are you syncing content from the iPhone to your watch, for example Music, Podcasts, Photos?