@sam14 , TurboTax is working correctly ---- (a) there is a safe harbor ( in not having to use the form 1116 and the limitation it places on the amount of allowable credit ) --- it is $300 for filing single and $600 for Married Filing Joint. Thus when you enter $600 foreign tax, TurboTax uses the safe harbor and not use the form 1116.. If you enter over $600 then form 1116 kicks in and the available credit is based on a ratio of foreign income to world income to allocate the foreign tax credit.
(b) you can also claim the foreign tax paid as a deduction , if you itemize ( but the SALT limits may kick-in )
(c) It may be simpler , especially if your foreign income is not going to increase year after year ( because you need foreign income to use up the foreign tax credit in future years ) to just enter the $600 as the foreign taxes paid -- there is nothing against not-recognizing some or all of the foreign tax.
That is my view
