per NJ:
If a nonresident employee works inside and outside New Jersey, only the compensation paid for work performed in New Jersey is subject to New Jersey withholding.
NJ-WT (state.nj.us) at. p. 6
The temporary relief period with regard to employer withholding tax for teleworking employees will end on October 1, 2021. As of that date, employers should cease sourcing income in accordance with the employer’s jurisdiction.
State of NJ - Department of the Treasury - Division of Taxation - COVID-19 Information - Telecommuti...
