I have a Mac running Catalina. It is almost new and I did not migrate anything from the old Mac, so should be a very clean install.
I installed Xcode 11 from the App Store. All fine.
Yesterday it wanted to update to Xcode 11.1. But the update took a long time and then failed. Try again later. I did. Same. The App Store UI gives you no clue what is not working.
I ran the Console app to check the log. Install failed “The package is attempting to install content to the system volume.”
Annoying. Suggested fix is to download the DMG. Another idea is to uninstall and then reinstall from the App Store. I like having it App Store managed so I did the latter and it worked.
Together with Gimp permission problems it looks like permission issues in Catalina are a considerable annoyance. Which is OK if security is better as a result; but that does not excuse this kind of arbitrary behaviour.