As you enter in any order:
the program keeps a running total and uses that until the maximum allowed of $10,000 for a married couple.
Once I hit the $10K, TT will not allow entry into any SALT type tax field. TT should accept ALL data and do the $10K cap calculations in a worksheet. It also appears that TT will not accept input of estimated/quarterly taxes paid in 2018 after I hit the $10K limit on SALT? This would be an error in the system.
@gordongrand It seems you have misinterpreted what was on the screen? So instead of dinging the answer, read the further explanation
TurboTax does indeed operate to limit the legal maximum deductible to the Federal government imposed limit of $10,000. You are indeed presented a screen that tells you this limit on deduction has occurred. However, reading the rest of the screen tells considerably more, and it helps to read all and not just some of what is on the screen.
What is does not tell you is that it is preventing you from having recorded the excess, and to say so is a misreading of the screen. In fact, for other purposes than the SALT limitation, those excess taxes paid are recorded and may be used in some other context.
READ the attachment and ALL of the Text in that first page!