I have tried all of these suggestions and nothing has worked.  No matter what I do, in Apple and/or in QB, nothing works.  I cannot change the date format in QB to anything other than YY-MM-DD which is not compatible with my Apple settings.  I have spent approx 20 hours over the last few weeks with Intuit "tech support" people;  none of them have been able to solve the problem.  Hoping you have some additional suggestions, AdonL...

If you can't change the date format to MM-DD-YYYY, my guess is that you live outside the U.S. and your Apple computer is picking up the format from your current location. Try this:

1. Go to Apple Settings > Date & Time > Time Zone and uncheck "Set time zone automatically using current location."
2. After unchecking that, from the "Closest City" dropdown menu, select a U.S. city (e.g., "Dallas, TX - United States").
3. Then, under Apple Settings > Date & Time, uncheck "Set date and time automatically." Set the date manually from the calendar and enter the time manually, which should match the time of the city you selected (Dallas, TX).

Once done, close Apple Settings, open QuickBooks, and try to record a transaction with an older date to see if it accepts the date.

If that works, you're all set! Just keep in mind that your computer will now show the time of the selected city (in this case, Dallas, TX) but at least you can record your transactions.

Hope this helps!