Watch
So is the Apple Watch series 3 useless since it can’t be updated
They can be updated. Is your iPhone updated to iOS 16.2? If you can't update your Apple Watch, you can take it to your Apple Store Genius Bar and Apple can update it for you.
Personally, I do update my hardware more often to stay current. The new watches do so much more than a Series 3 does. Whether you think its time to retire your Series 3 watch is up to you.