If your last pay period paid by that employer's ended in 2021, then he can report the pay period ending in 2021 as 2021 wage income.
If you are referring to Form 2555, Foreign Earned Income Exclusion or Deduction:
If you are excluding income based on the physical presence test, then as long as you can name a period of 330 days including just 2020 and then for your 2021 return you can name a period including part of 2020 and ending in 2021, you may still qualify for the 2555 foreign earned income exclusion for both years.
Please refer to the following for additional information:
IRS Instructions for Form 2555
