Apple does not make past, full-version installers of Pages available for direct user download. If you have never installed Pages from the Mac App Store, then you can use Pages for iCloud, but won't be able to obtain Pages for Mac — without an upgrade to Big Sur or later, hardware compatibility notwithstanding.
Alternatively, if you previously installed Pages from the Mac App Store, you can launch the Mac App Store (assuming Catalina), be signed in with the same Apple ID as used previously to obtain Pages, and then press cmd+0 (zero) to open the Purchased panel. If Pages is present with an Update button — click that. You will receive an initial dialog that you need to upgrade your operating system. Acknowledge that dialog, and do not click Cancel. If you are living right, a second dialog will now appear offering to install the last compatible version (11.1) of Pages for Catalina. You know what to do.