I am trying to download pages but it says I need mac OS 12 and my system update says I have the latest version of Big Sur 11.7.2. What can I do?

The current Pages, Numbers, and Keynote versions (12.2.1) in the Mac App Store require macOS Monterey or Ventura.

Have you ever installed Pages from the Mac App Store using the same Apple ID you currently use? If true, then launch the Mac App Store again signed in with that same Apple ID. Press cmd+0 (zero) to expose the Purchased panel. Pages should appear there with a blue cloud outline symbol. Click that and it will then offer to install the last compatible version of Pages for Big Sur.

However, if you never installed Pages, Numbers, or Keynote since Oct 2013 via the Mac App Store, then you cannot get any of these applications now for Big Sur.