Upgrading from an old Apple Watch to a new “Apple Watch Series 6” isn’t as easy as just buying one and putting it on. There’s not much more involved, but what you do have to do is important to get right, unless you enjoy exasperation.
Unpairing triggers a backup, which is what means you can restore your old settings to your new Watch
The problem is that the Apple Watch is still not yet its own, standalone device. While Apple has been steadily moving toward making it work entirely by itself, it’s still the case that your Apple Watch has to be securely paired to your iPhone.