@roalddahl14 , as I mentioned in your other thread , because you are a Resident for Tax purposes ( having passed substantial Presence Test [ SPT ] , based on the information you have provided), you file your return on form 1040 and are taxed on WORLD INCOME. Thus :
(a) while the work was accomplished before your becoming a Resident ,the payment received anytime after passing the SPT . So amounts received as Royalty in 2024 is recognized on your return for the tax year 2024, using Schedule-E ( page -2 ).
(b) Under the US-UK tax treaty, yes you could assert treaty article to reduce the double taxation bite.
If you need help on any of this , please consider writing back with exact situation/ questions.
You can also find the US-UK Tax Treaty text at : U.S.-U.K. income tax treaty, signed July 24, 2001, London (treasury.gov)
Namaste ji
pk
