reinstalling productivity software on iMac late2013 running Catalina10.15.7 OS

With the Mac App Store launched and you signed in with the same Apple ID that you used to install Apple's Pages, Numbers, and Keynote previously, press cmd+0 (zero) to open the Purchased panel and you should see a blue cloud outline with down-arrow adjacent to each of these applications. When you click these blue icons, you will be asked if you want the last compatible version (v11.1) of the application for Catalina. You know what to do and the applications will be installed.

The current v12.2 of these applications now requires that one has Monterey or later installed.

Is your Mac set up with the same Apple ID that you used before doing your fresh install of Catalina, and are you logged into the App store with the same Apple ID?

Also, I assume you had previously downloaded & installed Pages, Numbers & Keynote to your Mac before upgrading to Catalina. Is that correct?

Note that Apple persistently updates all its own apps with every release of macOS, requiring whatever is the current version of macOS in order to install or update its apps. As of Tuesday that would be Ventura. However, the App Store is supposed to allow you to download a previous version of an app if you are on a different release of macOS. Unfortunately I have never found that to work for me.