On January 8, 2024, the IRS released a notice describing many changes required to implement the Secure Act 2.0.
If you try to enter Code S for Box 12 of your W-2, you may see this message: "We're updating how SEP and simple plan contributions are reported on the tax return based on new guidance from the IRS."
Section 601 of the Secure Act 2.0 refers specifically to Simple and SEP Roth IRAs. Code S in box 12 defines how to handle a SIMPLE plan.
TurboTax is currently working on the issue. Please check back later after January 31, 2024.