Why does App Store start updating Xcode when latest version already installed?
Here is a tweak that you can try:


Go to Finder -> Applications
Move Xcode.app to trash. (Here it will ask you if you want to cancel update).
Agree to cancel the update.
Go to Trash -> Xcode.app, right-click and click on "Put Back"
Re-start using Xcode and continue with your work.


Also, while you wait for XCode to update and you are in a slow internet connection, go to https://developer.apple.com/download/more/ and download the latest version of XCode dmg using your Apple ID. The latest is 11.1 and they have 11.2 beta also.