I know how difficult this has been, @nonprofitmike. Let me share some updates about the investigation for getting an error when attempting to open your QuickBooks Desktop (QBDT) Mac file. 

Thanks for getting back here and sharing the details of the step you've performed as well as the outcome. I can see that you did everything you could to resolve this. Currently, the ongoing issue about the error when opening your file in QBDT Mac (INV-79008) is still ongoing. 

To further help you with this, I highly recommend reaching out to our Technical Support team. They can assist you in fixing this error so you can get back to work with your company file. You can also request a screen-sharing session so they can review your setup. Refer to the step below to contact them:

1. Access your QBDT Mac. 
2. Then, navigate to the Help menu and select QuickBooks Help.
3. Next, click Contact Us.
4. From there, enter a brief description of your concern and select Continue.
5. Log in to your Intuit account, click Continue and then select Continue with my account.
6. You'll receive a single-use code via. Enter it and select Continue (If you have more than one account, choose the account you want to use and then Continue).
7. Then, select to chat with us or Have us call you.

You can visit our support hours page to check when the support is available to ensure you'll get assisted immediately. 

I've also added this helpful resource that you can access at any time to get additional references and guides when performing your QBDT Mac tasks: QuickBooks Help page. 

Please don't hesitate to post again here if you have any other QuickBooks concerns. I'm always here ready to lend a hand to help. Have a good one and take care.