Which Line, exactly? Have you tried an entry using Forms Mode on the 8960 Worksheet or the actual form?
There are certain Form 8960 scenarios that require overrides (since they are not supported by TurboTax).
See page 15, https://digitalasset.intuit.com/DOCUMENT/A51oKyg2O/032522-2021-unsupported-calcs-L1FQfTTgn.pdf
