Your Mac is 64 bit.
Versions of macOS prior to Catalina could run both 32-bit and 64-bit.
With Catalina, the old 32-bit app interfaces were retired.
Your Microsoft Office was Office 2011, or older.
Versions of Office prior to 2016 are 32-bit.
Long unsupported and known to be buggy versions of Office, too.
Microsoft Office 2016, Office 2019 (full purchase), Office 365 subscription, and the (free) LibreOffice app are all 64-bit.
Purchasing Office 2019, subscribing to Office 365, or switching to LibreOffice, or maybe to the free Apple iWork Pages, Numbers, and Keynote apps—apps which can read and write many office documents—will get you going again on Catalina.