Unfortunately, this is one of the exceptions to the general rule that income is taxed when you receive it. The bonus will be taxable in NYC since it was earned for work performed in NYC, even though it was paid after you moved away.
What happens is, for your 2021 tax return, you will file a non-resident tax return for NYS, on which you report and pay NY taxes on your NY-source income only. If you also filed a tax return for your home state, you include the bonus as taxable income but your home state would give you a credit for the tax you paid in NY so you don't get double-taxed. But since you will be moving to Florida and Florida does not have a personal income tax, this won't be an issue.
