A rollover from the Roth 401(k) to the Roth IRA is indeed a distribution from the Roth 401(k). Because it's too late to obtain are return of the excess deferral, the deadline was April 15, 2023, the excess Roth 401(k) contribution and attributable earnings are, as you mentioned, taxable when distributed and are ineligible for rollover.
It's unlikely that TD Ameritrade will know anything about the excess contribution and be able to distribute the excess and attributable earnings to you as a taxable distribution instead of rolling them over unless you tell them about it. Even if you tell them they might not be able to do so and you would have to submit substitute Forms 1099-R to properly report the distribution. If the excess and attributable earnings end up the Roth IRA, they will need to be removed by a removal of excess contribution before the due date of the tax return, including extensions, for the year in which the deposit into the Roth IRA is made or treated as a regular Roth IRA contribution for the year in which the deposit is made.
