How to downgrade from Big Sur to Mojave on a 2014 MacBook Pro?

I do not advise you to downgrade from Big Sur to Mojave.

If you never installed Pages, Numbers, or Keynote from the Mac App Store, and they were preinstalled when you purchased the MacBook Pro, then you cannot obtain any versions of these applications now for any version of macOS earlier than macOS Sequoia v15.6. Apple does not maintain independent downloads of these past applications.

If you have installed these applications previously, then you should be able to get the last compatible versions of these for macOS Big Sur.

1. Launch the Mac App Store on Big Sur
   1. Sign in with the same Apple ID that you used to previously install these applications
   2. Use cmd+0 (zero) to open the Purchased panel of the Mac App Store.
   3. If you see Pages, Numbers, or Keynote present with a blue outline download symbol, or any indication that they can be installed, click that item.
      1. You may receive one or more dialogs. Do not click Cancel. The last dialog will ask you if you want to install the last compatible version for macOS Big Sur. You know what to do.

Have you tried Updating Pages and Numbers?

In theory, you should get updated versions of Pages and Numbers when you do that.

Open the Mac App Store and look for the Updates page.