I found the solution. I'm also a Mac user and was having the same issues. You'll need to go to the computer's system preferences to solve the issue.
Apple -> System Preferences -> Security & Privacy -> Privacy (I don't know if it'll automatically jump to that but there are 4 options at the top of the window that says "general, FileVault, Firewall, Privacy") -> Full Disk Access -> (if your lock is on for making changes (lower left of window), you'll need to unlock first) then scroll down the list of apps to Turbo Tax 2020 and select it -> reengage the lock for the window (if you unlocked it).
And then relaunch TurboTax 2020 via opening a file and then you should be able to save files again
