New York uses your total income to determine your tax rate, but then it applies that rate only to your NY income.
There probably isn't anything that needs to be fixed.
What you are seeing is accurate, but NYS is not taxing the income you made after you became a resident of SC.
Your total 2020 pay appears in the NY forms, summaries and interviews because NY uses your entire AGI to calculate your tax on NY income. They do this even if you were a resident of New York for 1 day.
It isn't, however, as bad as it appears. They calculate what your New York tax would have been if you earned everything in NY, but then prorate that tax based on how much of your income was earned while a NY resident.
For example, if the NY tax on your entire 2020 income was $10,000 but only 30% was earned as a NY resident, your NY tax would be 30% of $10,000 = 3,000.
Why do they do this? So they can tax your NY income at the highest possible tax rate, based on your entire AGI.
Thank you for your response. Just so I'm sure - NY uses my AGI, my deductions are applied to the AGI, and I am taxed at the remaining balance, which is more than I actually made in NY. Which also makes it so I made less money than last year, but am paying more in taxes.
NY determines the tax on your entire income for the year. Then prorates it based on the percentage earned in NY. Your tax rate may have increased.
For example: say you made $70,000 in 2019, taxed around 6%
Depending on your numbers, you could have made less money and paying more in taxes. NY taxes up to 8.82%.