how to reinstall microsoft office 2011 on a macbook pro 2020

Office 2011 is a 32-bit app. Newer macOS versions beginning with macOS Catalina no longer support 32-bit apps. macOS Mojave is the last version to support 32-bit apps. Going by the vintage of your MacBook, I believe it came pre-installed with macOS Catalina and may likely be running a newer version than that if you updated it.

With no 32-bit app support on recent versions of macOS, you are out of luck installing/running Office 2011. You also cannot install an older version of macOS on the MacBook than what came pre-installed on it.

I personally have a MacBook with Office 2011 already installed & running under macOS Mojave. This MacBook can be updated to a newer version of macOS but I am keeping it on Mojave to retain the use of Office 2011 (updating it will lose the ability to run it, even if it's already installed).

See: 32-bit app compatibility with macOS High Sierra 10.13.4 and later - Apple Support

Try using one of the built-in productivity apps that come free with macOS...Keynote, Numbers and Pages or try one of the free Office-like productivity suites like LibreOffice.