what 's next step with Turbo?
This has nothing to do with TurboTax at all.
if you get the message "TurboTax cannot be opened because Apple cannot check it for malicious software" then that is caused by the Apple "Gatekeeper" introduced with OS X 10.15 (Catalina).
That has nothing to do with TurboTax and will happen for any application not purchased from the Apple Store.
See this Apple article on this: https://support.apple.com/en-us/HT202491
And this TurboTax help article: https://ttlc.intuit.com/community/troubleshooting/help/turbotax-for-mac-won-t-open-when-installed/00...
For older Mac systems when TurboTax will not open.
Be sure that System Preferences -> Security & Privacy -> General -> Allow apps downloaded from App Store and identified developers is checked.
Go to the Applications folder and select the TurboTax application in the Finder and right click with the mouse (or control click) ans select the top "open". That should force the first open. After that it should open normally.