You will have to delete the old W-2 from your tax file - otherwise the program will continue to think you still work for that employer and keep asking you to report your 2020 income.
See: How do I delete forms in TurboTax Online?
Why does this happen? When you transfer the information from your prior year return, the program automatically includes certain forms in the current year - to make sure you don't forget to update those forms. If a form is no longer required (e.g. W-2s, 1099s, K-1s, Schedule C), you have to delete them from the current year.