“QuickBooks” can’t be opened because Apple cannot check it for malicious software.
Thanks for reaching out to the Community, @AndreCedars92. I'm here to lend a helping hand.
The error message you're receiving is caused by the Apple Gatekeeper introduced with OS X 10.15 (Catalina). In macOS Catalina and macOS Mojave, when an app fails to install because it hasn’t been notarized or is from an unidentified developer. Here's how to move forward in downloading QuickBooks Online App:
In the error message, select Show in Finder.
The Applications folder should open, and your QuickBooks will be selected. Right-click on QuickBooks, and hit Open.
A similar error message will appear saying, QuickBooks can't be opened because Apple cannot check it for malicious software. This time, choose Open and the program will properly install and open.
If the issue persists, I recommend contacting Apple Support for further assistance.
Let me know how this goes for you! I'll be on standby. Talk to you soon.