The way that you can check that your Roth withdrawal is not being taxed is by looking over your 1040 in print preview, line 5a and 5b. 5a will show the total amount of withdrawal, and 5b will be zero, assuming the Roth was the only withdrawal.
You don't need to enter the basis, because both basis and earnings can be withdrawn tax free once you've met the requirements (59 1/2 plus account has been open 5 years or more).
The withdrawal code on the 1099-R should indicate that it is a Roth, and then TurboTax Online will populate lines 5a and 5b properly.
@Sojo42 [edited 1/29/25 06:15 AM PST]
Roth 401(k) distributions will be on Form 1040 lines 5a and 5b, not 4a and 4b. The code-B Form 1099-R will have the taxable amount in box 2a and TurboTax will treat that amount as the taxable amount to be included on line 5b. The entire gross amount from box 1 will be included on line 5a.