Office 2021 is just the marketing name for the OTS version of Office. Office 365 (or now known as Microsoft 365) is just the subscription based service. They are the same version of the software. You register one with a product key (which is probably tied to your MS account for life) and the other is just tied to your MS account assuming you pay a yearly fee.
So at this point I think you are just getting mixed up with the naming. When you open your version of Office, does it have a product key listed? If so then that is the version you purchased at retail. If you go to your MS account you should see it listed as being retail as well. However if you look at your MS account and it is says there is an expiration date then that means you have an active MS 365 subscription as well. You would have had to buy that yourself.
Note that Windows 10/11 shipped with Windows Store versions of Office that were basically trial ware. To remove them you would use the Apps and Features option or just right click the tile icon and select Uninstall. These versions were designed to get people able to work with Office documents after installing Windows without having to also install Office. If you have a full copy of Office then these extra versions aren't needed.
Edge has nothing to do with Office. They are not related nor is WebView2. WebView2 is the UI component that wraps the browser and it is required in Windows. You don't have to have Office to get or use it. Again, they are completely unrelated. Most likely what is happening is that your Office addins or documents are trying to open HTML files and that requires a browser which is what would trigger Edge to start up. That has nothing to do with Office 2021 vs Office 365.