If your employer made the employer contribution to the designated Roth account in your 401(k), the employer is required to issue to you a Form 1099-R reporting the amount as taxable to you. If that employer contribution was deposited in 2024, you should have already received a code-G From 1099-R reporting in boxes 1 and 2a the amount of the employer contribution. (If that deposit was made in 2025, I believe that it will be on a 2025 Form 1099-R instead, but since the rollover of these funds to the Roth IRA happened in 2024, the deposit had to have been made in 2024 and you should have already received the code-G 2024 Form 1099-R.)
The procedure that the employer is to follow is to treat it as deposit to the traditional 401(k) account followed immediately by an In-plan Roth Rollover but without regard to any other funds you have in your traditional 401(k).
In this case, I imagine that that the code-G Form 1099-R would be issued by Vanguard on behalf of your employer.
This is all entirely independent of the subsequent nontaxable rollover to the Roth IRA that was reported on the code-H Form 1099-R.
