I tested code Z in box 12 in the TurboTax software for 2020 and got the same message that you are getting now for 2023. I also see that it's in the list of "Calculations Not Supported" at least as far back as 2015. If you have had this "for many years" I have to assume that you either entered it incorrectly, didn't see the message, or ignored the message.
I suggest that you consult a local tax professional.
