"Yet the IRS released 8990 and its instructions last December"

But there was a little change called the CARES Act that changed F 8990.  

THAT change hasn't yet been implemented, by the IRS and therefore, by Intuit.

Whether you can override that diag & still file is unknown.   I may try tomorrow; I have a return with a measly $ 160 that this issues is holding up the fiing.