From Amazon itself of a 3rd party seller that advertised on Amazon? Only Amazon is an authorized reseller other sellers are probably bootleggers.
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.
Purchased Mac Home and Business 2019 from Amazon. I hit download and it does that. However, there is no way to save the file. When I right click on the application to open, nothing happens. I have my software license, but there is no where to enter it. Amazon when through 3 support specialists and said to contact Intuit at this point. Please help