You don't need a script or plug-in. Just open preferences (Edit-Preferences) then search for " Bool Tool " in the Add-ons. Activate it. Now you can use the short cut (shift+control+B) or you can find it at the bottom of the object menu. It works for me in blender 2.91.2

You don't need to download a script or plug-in anymore, it's now shipped by default. 

Just open up the preferences (Edit > Preferences), search for "Bool Tool" in the Add-ons and activate it. Now you can use the short cut (Shift+Ctrl+B) or you can find it at the bottom of the object menu.

Further reading: https://docs.blender.org/manual/en/latest/addons/object/bool_tools.html