This is a good summary. I have on my list to also disable tabbed windows, which @IntuitBrooks shed light on (I'm using QBDT 2021):

1. Hold down the option key while launching QuickBooks. This prevents QuickBooks form opening your previously used company file.

2. Select your company file from the "No Company Open" Window.  Hold down the command key while opening the file. This prevents the last used windows from opening.

3. Go into QuickBooks->Settings… Select the Toolbar & Tabs icon in the 3rd row down and then uncheck the Use Tabbed Windows checkbox.

4. Avoid opening the home page.

I was able to run invoices last night and pray when the update arrives all the data is preserved. For those users on older versions of QB for which there is no upgrade path I hope Intuit provides you with some kind of a discount since this incompatibility was unforeseen.