The last compatible version of Pages, Numbers, and Keynote for Catalina is v11.1. Apple now requires macOS Big Sur or Monterey to install v11.2 of these applications which are currently available in the Mac App Store.
On Catalina, launch the Mac App Store and be signed in with the same Apple ID as you used to install Pages previously. Press the cmd+0 (zero) keyboard sequence to open the Purchased panel. If Pages is there with an Update button, click that. A dialog will appear stating that you need a newer version of macOS. Acknowledge that dialog without clicking Cancel. A second dialog may appear offering to install the last compatible version of Pages for macOS Catalina. Accept that, and you should then have Pages v11.1 installed. Repeat for Numbers and/or Keynote.