I can't update pages on my Mac book pro mid 2012

If you never installed Pages from the Mac App Store on your Mid-2012 Mac Book Pro, then you simply cannot get Pages for macOS now, as it requires macOS Big Sur, or Monterey. You would have to continue working on it with the iPad, or via Pages for iCloud.

If you had installed Pages previously from the Mac App Store, then you might be able to obtain the last compatible version of it for your current operating system version on the Mac. Try the relevant following paragraph depending on whether you are running macOS Mojave, or High Sierra.

Launch the Mac App Store on the Mac. Sign in with the same Apple ID as you used previously to install Pages. If you are currently using macOS Mojave (10.14.6), the press cmd+0 (zero) to open the Purchased panel, and if Pages appears there with a download feature, click that. You will be advised that you need a newer version of macOS to get the current Pages, and acknowledge that without clicking Cancel. A second dialog panel should appear offering to install the last compatible version of Pages (v10.1) for macOS Mojave.

If you are using macOS High Sierra (10.13.6), launch the Mac App Store in the same manner and Apple ID as in the previous paragraph. Press the Option key while clicking the Purchased tab on the application. This will present prior installed applications, and if Pages appears there with an Update or Install button, click that. The last compatible version of Pages would be 8.1 for High Sierra.

There might, & it's a big "might," be a workaround to getting a compatible version of Pages, as well as Numbers &. Keynote, on your MacBook Pro. There is absolutely no guarantee that this will work but I do remember a similar workaround in the early days of the pre-2013 iWork apps when they first became available in the Mac App Store.

First, you would need to "purchase" Pages in the Mac App Store using your Apple ID on a Mac running Big Sur or Monterey. Once you have done that you can follow Viking's steps to see if that purchase would now be recognized on your Mac running an older version of macOS.

Also, be aware that if you using a version of Pages on your Mac that pre-dates the current version on your iPad, you may not be able to work on the files last saved on an iOS device or in iWork for iCloud. Current compatibility is no guarantee of future compatibility. I was just able to open a small test Pages file created on my iPad mini with Pages 8.1 on my Mac mini running Mojave. The Mac App Store will not allow me to update to a newer version on this Mac.

You are welcome.