UPDATE as of February 5, 2022.
After two MacOS updates, and at least three updates to the TurboTax software, TurboTax 2021 finally transferred the data from my prior year's (2020) TurboTax file into the 2021 TurboTax return.
I wish I could explain what specifically happened to cause it to finally work. My only suggestion is to make sure you are using the latest MacOS and have allowed TurboTax to download and install its latest version (which for me is TurboTax Version: 2021.r15.074 and MacOS Version: Monterey 12.2)
