At the same time, Turbotax has a list of forms that are unsupported, and 8978 is *not* in that list. See https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-forms/irs-forms-included-turbotax/L5KYwBrRH_US_en_US.
I assume from the Turbotax list that 8978 should be supported since it's not on the list of unsupported forms. However, I suppose it is possible that the Turbotax list is incomplete.
The list is incomplete.
See this TurboTax website for federal and state forms availability, Form 8978 is not listed - https://form-status.app.intuit.com/tax-forms-availability/formsavailability?albRedirect=true&product=Turbotax_online&bu=cg
Disappointing, but at least it's good to have a clear answer. Thanks.