@TaxGuyBill thanks your help.

For 2023 and 2024 client been working as a physician assistant and already announced to all employers do not issue 1099-NEC under my name for 2024. Around January 2024 he contributed on Roth 401-K and Solo401-K under his name for the year of 2024. (same description: 2024 employee contribution)

Since he will not have any 1099-NEC under his name, so we will not make any Sch C for him based on net income and consider solo 401-k as well, just he will have a W-2 from his S-Corp for 1040 and 1120-S , now I think he should cancel recent solo 401-K contribution under his name? Am I right?  

and run 401-k through the payroll because he wants to have a employee for 2024.