I don't know how it is for other state, but for New York, that link you posted has the wrong information.
It says:
If your state is one of those states that has a 529 plan deduction, TurboTax will prompt you to enter your 529 contributions when you get to the credits/deductions portion of your state tax interview.
In Turbotax 2020, For New york state tax, you have the following sections/portions:
==================
General Information
New York City and Yonkers Information
Changes to Federal Income
College Tuition Expenses
Credits and Other Taxes
Other Forms and Voluntary Contributions
Your New York Numbers
Recent Events
===================
The New york 529 information is NOT in the 'Credits and other Taxes' section.
It is in the 'Changes to Federal Income' section.
