That’s good, the not so good news is that Apple has made it tougher to get other releases from the App store. I assume you launched the App Store, clicked on your account and looked under purchases? Did you check in the update section of the App Store? If you can’t find it in either of those two spots, then go to the Catalina Unsupported thread. They should have a link to the App Store so you can download it again.
If you can’t find it there then ask. I was able to get it for my 2012 Mini but unfortunately I forget how. I don’t remember if I did it via an internet restore. You want to try that first and see if Catalina defaults on an internet restore. And you will know right away because you will see the Catalina icon when attempting an internet restore. Don’t worry as you can always back out but as is always the case make a backup just in case.
Edit: I found this link.
https://support.apple.com/en-us/HT211683
Double Edit: Yup I just tried it and it works. Scroll down the page and click on the Catalina Link and it will open the App Store and you can then download Catalina.