I have had SUCCESS with e-filing my 2020 Taxes using TurboTax Deluxe and my older MacBook Pro (running OS Catalina)!!! I, too, have battled the inability to save updates to my return, culminating in the inability to eFile, but I got it work without contacting Turbotax or Apple.
Here's what worked for me:
1) do all of the work up to filing. If you have to stop and start, save. Actually, it would be smart to save to a USB drive as you go, especially nearing the end of your process.
2) print before you file (just in case!) then go through all of the steps to E-file. If it works, great, but if it refuses to save and then E-file because your "file is locked" or "you do not have authorization to open this file" or some other silliness, then begin the process below:
3) when you are sure that you are ready to E-file (no last-minute tweaks or further reviewing) go to "Duplicate" (part of TurboTax drop down menu near the top left corner of the computer screen -- to the right of the Apple logo). This will create an untitled copy of your tax return -- with everything that you have entered into it up to this point.
4) working from this untitled Turbotax document (that by now has everything, including any bank routing numbers, your email, and all of the final details for submission), GO STRAIGHT TO FILE. (Within the TurboTax program -- the top right option on the TurboTax screen).
4) walk through the steps to file your return, but Do NOT SAVE until you absolutely have to
5) when you press the last submit button, a "Save As" will pop up.
6) give your Tax return a name and whatever encryption you need to give it, and SAVE IT TO YOUR DESKTOP.
7) for me, the moment it saved to my desktop, it began the (successful) submission process.
It only took about 7 attempts for me to try this and have it work. I hope that it works for you, too, and saves you some time!
