Source: Apple
A few older iPhones will no longer be able to update to iOS 16. iPhones introduced in 2016 or earlier will not be getting Apple software updates. These include the iPhone 6S, iPhone SE, and iPhone 7. It's not an unexpected move, given Apple will regularly retire software support for older devices. If you have one of these devices, it doesn't mean you can't use them anymore. It just means you won't get the fancy new features.
What's more important for deciding to switch is whether you'll lose access to security updates. Right now, Apple still offers security updates to older iPhones like the iPhone 5 and 6. But as CNET pointed out, these updates only address critical vulnerabilities, so you could still be vulnerable to other attacks. Regularly check Apple's Security Updates page to stay on top of the security updates you're getting.