What he filed for 2022 does not create any requirements for 2023. But as long as he remains a New Jersey resident he must file a New Jersey resident tax return. All of his income is subject to New Jersey tax, no matter where the income is from.
For 2023 he must file both an Illinois nonresident tax return and a New Jersey resident tax return. The income from working in Illinois is subject to Illinois tax because that's where he worked, and also to New Jersey tax because he is a New Jersey resident. He will get a credit on his New Jersey tax return for part or all of the tax that he pays to Illinois.
