@RC519 , I am unable to reproduce what you are describing. TurboTax does propagate the amount from box 5 to your basis in Roth IRA contributions on the IRA Information Worksheet as required but has no effect on tax liability (except possibly lowering tax liability if one separately enters a code-J or -T Form 1099-R for a distribution from a Roth IRA). If you fail to enter the box-5 amount, TurboTax will not track your Roth IRA contribution basis correctly (unless you correct it manually) and that could affect the calculation of the taxable amount of nonqualified Roth IRA distributions this year or in the future, if any.
The plan administrator is required to track Roth 401(k) basis. The payer should always show an amount in box 5 of a code-H Form 1099-R so that the IRS will know the amount of contribution basis that transfers to your Roth IRA in case you ever make nonqualified Roth IRA distribution. When the tax code reverts after the year 2025, it could also affect whether you qualify for a deduction for unrecoverable basis if your investments lose value.
Since there is no tax withholding shown, yes, you can omit the amount from box 5 as long as you separately correct TurboTax's tracking of your Roth IRA contribution basis. With no tax withholding, the Form 1099-R details are omitted from your e-filing, so the IRS won't know the difference.
