UK ISA foreign investments

Hi, I have a UK stocks and shares ISA although T212.
I want to invest in some Canadian and US stocks but want to check whether I have to make any specific declarations etc for tax purposes, and if so - how do I do this?
The site has not notified me that it is necessary.

It did on sign up. You’ll have completed and signed a W8-BEN. Unless you specifically remember not filling this out.

Not too long now… :point_up: The United States of Eh-merica