Some adjustments to Form 8960 need to be made in Forms Mode (on the worksheet) and Forms Mode is not supported in the online versions of TurboTax.
Further:
Net Investment Income Tax (Form 8960): The program does not automatically support the
following scenarios for the calculation of Net Investment Income Tax (NIIT). Make any necessary
adjustments on the Form 8960 worksheet:
Any adjustment to the gain or loss from the disposition of an interest in a partnership or S
corporation that should be included on line 5c.
Activities involving trading in financial instruments or commodities which should be
included in NII regardless of material participation.
Any adjustment to interest or dividend income or to capital gain/loss that is not related to
an activity.
Net operating loss for NIIT purposes.
Any other adjustments or deductions not accounted for on the Form 8960 worksheet.
See https://digitalasset.intuit.com/DOCUMENT/A51oKyg2O/032522-2021-unsupported-calcs-L1FQfTTgn.pdf
