where do i enter my contributions for 2024 to a 401K?

In TurboTax, you do not need to enter contributions you made to your 401(k) plan at work.

These contributions are already reported on your form W-2 in box 12 with code D and have already been excluded from taxation in the amount reported in Box 1 of your W-2.

Please check that your W-2 has the amount of your 401(k) contributions in box 12 code D and enter your W-2 in TurboTax as received.

The contributions you made to the 401(k) are on your W-2 in box 12 with a code of D.  You do not enter the contributions anywhere else on a tax return.

If you are a W-2 employee, your 401k contributions are on your W-2.   (Usually in box 12)   When you enter all the boxes from your W-2, you are done entering anything about the 401k.   You do not enter it anywhere else.