I'm fairly certain this is, indeed, a software bug on TurboTax's end.
As per their own guidance, under the Videos section, "Video: One Big Beautiful Bill: New Car Loan Interest Deduction (Part 4)"
"At $200 for every $1,000 over the limit, rounded up, that works out to $2,600 off your deduction, assuming you paid at least $10,000 in interest, your maximum deduction is $10,000 minus $2,600, which equals $7,400."
Their calculations are currently deducting from the interest paid, plus the maximum allowable deduction.
