Since upgrading my macOS to 10.15.7 I can no longer open Microsoft Word.

If you subscribe to Microsoft 365, have a look at this link. I downloaded and installed the file that contains Word, Powerpoint, Excel and Outlook, and they work just fine. As far as I can see, the only drawback is that Microsoft keeps telling me that updates are available, presumably for updated versions of the apps which, of course, do not work on Catalina.

https://answers.microsoft.com/en-us/msoffice/forum/all/office-365-on-mac-os-catalina/82b8e0c3-d364-4bb3-82e3-5c291ff0ac42

The 32-bit versions of Office 2011 and 2016 for Mac are not supported on macOS Catalina, and as Microsoft no longer supports Catallna for new installations/updates of currently supported Microsoft 365 and Office 2021 for Mac, you will need to consider a third-party Office clone to continue working on your existing Office documents. Some options:

• The free LibreOffice suite and documentation
• The paid, but with free trial, Softmaker Office 2021 for Mac.

If you never installed Apple's Pages, Numbers, or Keynote applications from the Mac App Store since Fall 2013, then you cannot get these for macOS Catalina. If you have, then you can get older versions of these Apple applications that were compatible with Catalina, though as they are not clones of their Microsoft counterparts, you may have used features in your existing documents that Apple's applications cannot translate on opening.