Is it worth upgrading?

iPhone 12 and iPhone 13 can handle much faster 5G cellular. The iPhone 11 cannot.

That alone may be mighty important for a lot of users. If 5G is not important to you, or not important at this time, then it would probably make sense to get a few more years use out of the iPhone 11.

That's entirely up to the user. My iPhone XS serves me well and I will not upgrade it until it dies. Its battery health is at 83% and still gets me through a day easily. Other people may want new features that are only available on newer model iPhones.

Unless Apple offers a new feature-rich iPhone with a 3.5 inch (or smaller) screen. Then I will jump on it.