I need to download Pages, IMovies and Keynotes into my iMac 2012 Catalina OS

The current versions of Pages, Numbers, and Keynote (v11.2) in the Mac App Store require that you are now running macOS Big Sur as a condition for installation. The current version of iMovie (v10.3) in the Mac App Store now requires macOS 11.5.1 or later. These will not install on Catalina.

Apple does not provide individual user downloads of past, full installer versions of these applications for Catalina.

If you ever installed these applications, the Mac App Store, and you are signed in with the same Apple ID, the store may have a record of it in the Purchases panel which you access with cmd+0 (zero). If the applications are present with an update button, click that. You will be greeted with a dialog that the application(s) require Big Sur, and then just maybe, it will offer to update your selected applications to the last versions for Catalina. Don't get your hopes up that this will work, but its worth a try.

Failing all above, then you can only use Pages/Numbers/Keynote for iCloud, or the respective iOS/iPadOS applications on 14.8, or 15.0.2 or later.

Enable iCloud Drive on the Mac side and under iCloud Drive -> Options… select Pages and Keynote. This will expose a Pages and a Keynote folder on iCloud Drive. With your AppleID, sign in to iCloud dot com and then you can create/edit/download Pages or Keynote documents there. Also, on the Mac side, you can visit Finder Preferences > Sidebar, and enable iCloud Drive there so it will show up in the Finder sidebar.

Pages User Guide for iCloud

Keynote User Guide for iCloud

Open the AppStore & sign in, then in the search bar type...

Pages

To start with.

Ah, Apple doesn't like old versions, if that is what you need.

They aren't listed under Purchased perchance?