Microsoft 365 can't use.

Older versions of Microsoft Office (2011 and older as well as early versions of 2016) are not compatible with Catalina macOS 10.15. If you are paying for a Microsoft 365 subscription, you can upgrade to the current version of Office which is compatible with Catalina. See: https://support.microsoft.com/en-us/office/how-do-i-upgrade-office-ee68f6cf-422f-464a-82ec-385f65391350?ui=en-us&rs=en-us&ad=us#OfficeVersion=Microsoft_365

If you have an older version of Office but don't have a current Microsoft 365 subscription, see the following options:

If you have an early version of Office for Mac 2016, you can update it at no charge. See: https://docs.microsoft.com/en-us/office365/troubleshoot/administration/office-2016-for-mac-64-bit-upgrade

If you have Office for Mac 2011 or earlier, you can either subscribe to Microsoft 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

Or use the free Microsoft Office on the web: https://products.office.com/en-us/free-office-online-for-the-web

Or Google Docs: https://www.google.com/docs/about/

Other options include using the free and very good Libre Office https://www.libreoffice.org/

or Apple's Pages and Numbers

Have you notified Microsoft or look at their support site.