Get your taxes done using TurboTax

This is an apparently widely encountered defect in TurboTax. Here's a sampler of the numerous reports:

https://ttlc.intuit.com/community/taxes/discussion/can-t-save-document/00/1068534
https://ttlc.intuit.com/community/taxes/discussion/error-message-that-says-my-return-cannot-be-s[pro...
https://ttlc.intuit.com/community/taxes/discussion/how-do-i-save-turbotax-2019-on-mac-keeping-gettin...
https://ttlc.intuit.com/community/taxes/discussion/re-having-problem-saving-document-says-that-i-don...
https://discussions.apple.com/thread/4712960

POSSIBLE SOLUTION: It appears that TurboTax fails to request "full disk access." You have to go into System Preferences / Security & Privacy and give TurboTax full disk access. I don't know why it's allowed to initially create the file but then never update it, but that's probably an Apple issue.