How to uninstall Zoom outlook client from outlook 365 from Mac
I found it! The zoom plug-in / add-in is not provided by the Microsoft store, rather installed by zoom itself, so you won't find it in the Microsoft store > my add-ins area. If you go to finder > applications, you will see a folder called 'Zoom plugin for Outlook', in that folder is an uninstall icon. Close outlook, uninstall, and voila....zoom gone! 

This has been especially important since the zoom client no longer works in macOS Catalina, so it's useless to keep it in outlook.