microsoft office 2011 on Big Sur

As Yer_man says: Office 2011 doesn't work on BigSur, because it is a 32-bit app. It won't run on Catalina too. If you don't want to buy a new Office version or subscribe to Office 365, you can use the free OfficeLibre for Mac. https://www.libreoffice.org/get-help/install-howto/macos/ It works fine together with Office docs.

Another alternative (it depends on your needs) is Apple's own Pages, Numbers and Keynote (also free)

Office 2011 won't run on Bug Sur. You'll need a more recent version of Office or one of the Office substitutes.