Because the April 1, 2023 deadline has passed for notifying the employer to be able to obtain a corrective distribution, the excess amount and any earnings attributable to the excess amount are deemed to be the first amounts distributed and are taxable when you later take any distributions from the Roth 401(k). These amounts are not eligible for rollover. To accomplish this, the amount of the excess and the attributable earnings must be tracked separately from the other amounts in the Roth 401(k), so it probably means that the plan needs to track these amounts. See "Designated Roth Contributions as Excess Deferrals" in Treasury Decision 9324 Internal Revenue Service 2007-22 I.R.B. 1302. Also see CFR 1.402a-1 Q&A-2(c) and Q&A-3:
https://www.law.cornell.edu/cfr/text/26/1.402A-1
