Found more info from internal revenue bulletin:

https://www.irs.gov/irb/2024-02_IRB

Designated Roth matching and nonelective contributions are includable in an employee’s income when made. However, SECURE 2.0 doesn’t specify how or when to report these amounts for income tax purposes (e.g., as Form W-2 wages or instead on Form 1099-R). The law also doesn’t say whether these amounts are subject to Federal Insurance Contributions Act (FICA), Federal Unemployment Tax Act (FUTA) or federal income taxes. Notice 2024-2 provides clarification on these issues.

• Includable in the year of allocation. The notice confirms that designated Roth matching and nonelective contributions are includable in an employee’s income in the year the contributions are allocated to the employee’s plan account. This treatment applies even if the contributions are deemed made on the last day of the employer’s prior tax year for the employer’s tax purposes.
• Reportable on Form 1099-R. Designated Roth matching and nonelective contributions are reportable on Form 1099-R. IRS instructs filers to report the aggregate amount of such contributions made to a participant during the year in boxes 1 and 2a and use code G in box 7.
• No federal tax withholding. Designated Roth matching and nonelective contributions are excluded from wages for federal income tax withholding purposes. However, IRS indicates that employees electing Roth treatment may need to adjust their tax withholding elections or make estimated tax payments to account for the tax due on these amounts. Sponsors may want to communicate this point to eligible employees.
• FICA and FUTA treatment. Like matching and nonelective contributions made on a pretax basis, designated Roth matching and nonelective contributions under qualified and 403(b) plans aren’t wages for FICA or FUTA purposes. Designated Roth matching and nonelective contributions made to an eligible governmental plan aren’t wages for FUTA purposes but sometimes may be FICA wages.