I believe all employer contributions that are 100% vested can be elected as ROTH which would include safe harbor contributions. I think the 100% vesting of employer ROTH is because the employee is paying the taxes on 100% of the contribution so the IRS doesn't want forfeitures of ROTH.
And while it's technically currently available, there is no IRS guidance that I am aware of on how the income is reported to the employee and what withholding rules may apply. So I'm not sure if anyone is currently doing this.
Seems like it would be 1/1/2023. The participant didn't complete the requisite number of hours in their first eligibility computation period, so the eligibility computation period switches to the plan year. The first plan year in which they completed 1,000 hours of service was 2022. So they enter 1/1/2023.