Pages, Numbers, Keynote

If you have never installed Pages, Numbers, or Keynote from the Mac App Store, then you are done as the current versions require macOS Big Sur (11.*), or Monterey (12.*) to be installed beforehand.

If you have installed these applications from the Mac App Store in the past, then launch the Mac App Store and sign in with the same Apple ID that you used to install them before. Press cmd+0 (zero) and a Purchased page will appear. If these applications are present, they will have a blue outline cloud with down-arrow next to them. For each of these applications, click that icon, and a panel will appear offering to install the last compatible version (11.1) of these applications for macOS Catalina.

Your only option on your Mac is using Pages, Numbers, and Keynote for iCloud via Safari browser. These iCloud applications should have access to your documents created on your iPhone via iCloud Drive. You can then download the results as Word, Excel, Powerpoint, or PDF documents to your Mac for use in a third-party Office suite.

The purchase page on the iOS App Store is not related to the Mac App Store on the Mac. As you stated you had never installed Pages, Numbers, or Keynote previously on the Mac, their current operating system requirement is that you must be running macOS Big Sur (11.*), or Monterey (12.*) to download these applications. Your MacBook Pro is too old to install either of these newer operating systems, so you cannot get the applications.