Download NEW copy of Catalina
How do. I download a fresh copy of Catalina to replace my current copy that is not working?
MacBook Pro 13″, macOS 10.13
Open your Safari browser, do not use Firefox and click on this link.
How to upgrade to macOS Catalina – Apple Support
go to Section 4 and click on Get macOS Catalina, this will redirect
you to the App Store Catalina download page, it should say Get or
Download.
If the App Store says ‘Open’ then it is detecting a previous download of the install app
go to the Applications folder locate Install macOS Catalina.app.
Move it to the Trash, empty the Trash.
Restart, click on the link again, the App Store should say ‘Get' or 'Download'.