Where in Turbotax do I enter the amount of federal withholding from my IRA withdrawal?

The federal taxes withheld are reported in box 4 of the Form 1099-R that you received.  Enter your Form 1099-R on your tax return.  The amount from box 4 of the 1099-R flows to the federal tax return, Form 1040 Line 25b.

To enter, edit or delete a form 1099-R -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button

Or enter 1099-r in the Search box located in the upper right of the program screen. Click on Jump to 1099-R

Online editions -

On the screen Did you get a 1099-R in 2024? Click on Yes

On the screen Let's import your tax info Click on Change how I enter my form
On the screen How do you want to add your 1099‑R? Click on Type it in myself

On the screen Who gave you a 1099-R? select the type of 1099-R you received and Continue