You have always been able to enter a six-digit IP ----
If you have a 6 digit PIN issued to you by the IRS you need to enter it in order to e-file. Go to Federal>Other Tax Situations>Other Return Info>Identity Protection PIN and enter the six-digit PIN.
As @xmasbaby0 stated, TurboTax does handle the entry of an IP PIN. Are you referring to an IP PIN you received this year, 2024? The 2024 IP PIN is good for any Federal return filed in calendar year 2024, including prior-year returns filed this year. A new IP PIN is required every calendar year. So a new 2025 IP PIN will be required beginning January 1, 2025. If you opted-in proactively to the IP PIN program, your 2025 IP PIN may not be ready for retrieval online until mid-January or so. On the other hand, if it was the IRS that is requiring you to use an IP PIN because of confirmed tax-related identity theft that they investigated, they should mail a notice each year in December or January containing the new IP PIN, but it should be available online, too, if the notice is not received or lost.
Even if you are not efiling, you should still enter the IP PIN on your return (TurboTax will do it). Otherwise your paper return could be subjected to extra scrutiny and additional ID steps.