Where can I find standard high school textbooks used in the US and UK? So for example, India has this government organization called The National Council of Educational Research and Training (NCERT). They produce their textbooks which are also available to download for free here, for the grades 1-12 for all subjects. From my experience they are one of the highest quality textbooks in India.
Similarly, where can I access such textbooks which are of the highest quality, and are used in the US and/or UK? I'm mostly interested in searching for textbooks for the grades 8-12. I want to get a flavor of what kind of education do students get exposed to in the US/UK and I plan on reading their textbooks for the grades 8-12.
In the US, at least, some of the states have lists of approved books. Texas for example has a list: https://repositories.lib.utexas.edu/handle/2152/19095
Maryland, or at least some large counties there, may also have such an approval process.
There are probably others. But note that some of the textbook selections in Texas are very controversial, as the selection board is sometimes dominated by creationists and other science deniers. So, use caution with this list and any other.