Re: Dear Google . . .
RCS originally did not include E2E encryption, but Google Messages added support in late 2020; Group messages got E2E encryption this year.
6 publicly visible posts • joined 1 Dec 2011
Scripts trying to access a frame's content are subject to the same-origin policy, and cannot access most of the properties in the other window object if it was loaded from a different domain. This also applies to a script inside a frame trying to access its parent window.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/iframe#Scripting