Catalina and beyond do not support 32-bit applications, and Microsoft's only supported 64-bit applications now are the subscription Microsoft 365, and the single-purchase Office 2019 for Mac.
The fact that you once paid for Office 2011 for Mac is now an irrelevant factor on an operating system that no longer supports 32-bit Office suites and Office 2011 for Mac was retired in Oct 2017. Now, if you want to install supported, 64-bit Microsoft applications, you have a choice of the subscription Microsoft 365 or the single-purchase Office 2019 for Mac. You should note that Office 2019 for Mac will be replaced with the forthcoming single-purchase Office 2021 for Mac this Fall.
Your non-Microsoft options are the free LibreOffice Suite, or the paid, but less expensive SoftMaker Office product. Neither of these provides an email client if you are dependent upon OutLook. Either of these linked solutions will open your existing MS documents.