Only foreign income is (US taxed) share dividends

Living on a small private pension (PAYE), I haven't filled out a tax form in years. My income from foreign dividends is now above the (equivalent) of £1000 (2023 - 2024), so I assume I have to complete a self assessment form just for this?, and how does that work if they have already been taxed by the US? (I have a W-8BEN)

Hi,
Please refer to the link below for guidance:
Tax on foreign income
Thank you