Green card holders are considered US residents. Your worldwide income is taxable. You can claim a credit for tax paid to the UK on income taxed by both countries.
Where do I enter the foreign tax credit (Form 1116) or deduction for 2021?
How you receive your money (UK bank account) does not affect your tax obligations, except you may fall under foreign bank reporting requirements.
Report of Foreign Bank and Financial Accounts (FBAR)
Your employer would not have to withhold US tax or due any sort of reporting if they are not conducting business in the US. If they were, they would need a US tax ID number.
Whether your employer owes US tax depends on what they are doing business in the US. You don't say what you do.
See 26 CFR § 1.864-4 - U.S. source income effectively connected with U.S. business.
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