The last Apple branded "iWork" suite (e.g. the retail iWork '09 DVD) was 32-bit and not supported after Mojave. Catalina and later only support 64-bit applications.
If you never installed Pages, Numbers, or Keynote from the Mac App Store since Oct 2013, then you cannot get them now for Catalina as current versions (v13) presently require Monterey or later.
If the second paragraph is false, then on Catalina, launch the Mac App Store and sign-in with the identical Apple ID used to previously install these applications since Oct 2013. Press cmd+0 (zero) and look for the following symbol adjacent to all three applications:
if present, click that icon and you should see a dialog offering to install the last compatible version (v11.1) of each application for Catalina.