If you have previously installed Numbers on an older version of macOS via the Mac App Store, then you can get Numbers v11.1 for Catalina. If you never installed it before, there is no means to get it now for Catalina.
Launch the Mac App Store on Catalina. Sign in with the Apple ID that you used to install Numbers 3 or later on the older Mac. Press cmd+0 (zero) to open the Purchases panel. There should be a blue outline cloud symbol next to Numbers — click that. There may be one or more dialogs (or sheets that descend) and you do not click Cancel on any of these. One will offer to install the last compatible version of Numbers for Catalina.
If you cannot get Apple's Numbers, download LibreOffice 24.2.1 and use its Excel-clone Calc spreadsheet.
Microsoft only supports Microsoft 365 or Office 2021 for Mac now on Ventura or later.