All your income is taxable to New York if your employer did not change your "work location" to Pennsylvania after you moved to the Keystone State.
New York follows the convenience of the employer rule and says, "If you are a nonresident whose primary office is in New York State, your days telecommuting during the pandemic are considered days worked in the state unless your employer has established a bona fide employer office at your telecommuting location."
Your income will also be double-taxed from the point you become a PA resident, though you can claim a credit on your PA return for tax paid to NY.
You should allocate your bonus to your state of residence at the time of receipt, which sounds like NY.
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