I'm happy you find QuickBooks amazing and I appreciate your interest to continue using our product.
Mac OS X "Panther" 10.13 or newer (like macOS Catalina) is one of the recommended specs you need to get the best out of your QuickBooks experience. To learn what computer and browser you need to access QuickBooks Self-Employed, check out the System requirements link. It's important to check your computer's specs to avoid issues in the long run.
I'd also like to know if you're referring to QuickBooks Desktop (QBDT) for Mac 2011 since we've already discontinued the service. You'll want to use QuickBooks Desktop for Mac 2019 (R7) or 2020 (R2 or later) so you can work with macOS Catalina.
Let me know if you have follow-up questions, and I'm always around to help you out.