What Pages were you using that disappeared on Catalina? Pages '09 (left), or the new Pages on the right?
If Pages '09, it is a 32-bit application and is unsupported on Catalina. If the other Pages, do you have it backed up on a Catalina Time Machine backup, where it may be retrieved?
If not the previous, see if you can get it back by launching the Mac App Store, ensure that you are signed in with the same Apple ID as you used to originally download Pages. Press cmd+0 (zero) to open the Purchased panel, and if the Pages application has an Update button or cloud symbol, click that. You will receive a dialog stating that you need macOS 11 or later to get the current Pages version from the Mac App Store. Once you click that, you may receive a second dialog offering to get the last compatible version of Pages for Catalina. Click that and if you are lucky, you will end up with Pages v11.1 in your /Applications folder.
Apple purposely made Pages (easier) to use than third-party word processing applications as it was intended for consumer usage and easier meant omission of more powerful features. Knowing how you used Pages and the features you require may help in a substitution answer, but know that Pages documents can only be opened by Pages, and any other word processing application expects Microsoft Word documents.