Finish updating your Catalina to 10.15.7 and any available browser and security updates that may be pending.
If you previously installed Pages/Numbers/Keynote since Oct 2013 from the Mac App Store, you can get the last compatible versions (11.1) of these applications for macOS Catalina. Launch the Mac App Store and sign in with the same Apple ID that you used previously to install these applications. Then press cmd+0 (zero) to open the Purchased panel and if the three applications appear there, click the blue cloud icon that will install them again. A dialog will appear offering to install the last compatible versions for Catalina.
If you never previously installed these applications from the Mac App Store, then you cannot get them now as Apple does not provide other means to download them. You would need to use the respective iCloud applications to open existing or create new documents.