When I went through high school, there were two options for satisfying the Government portion of our social studies requirement:
American Government was for Juniors and Seniors. This was the more popular of the two options given how full my section of the class was. Like
@heathercho , we learned about the Constitution, separation of powers, the bill of rights, other essential amendments, and how Congress operated -- including the different forms of vetoes -- along with a brief side lesson on parliamentary procedure and Robert's Rules of Order. We also learned some simple law stuff such as the impact of ex post facto laws and bills of attainder. About the only complaint I might have in retrospect is that we covered enough topics that it was difficult to really get into any of the them on a deeper level due to the time constraints associated with a one-semester class.
Fundamentals of Government was a class intended for Freshman (and maybe Sophomores) that wanted to meet their Government requirement immediately and not wait until they had upper class status. I have no idea how the course was structured, but I suspect it was a lite version of American Government in that it covered the same topics but perhaps with less detail and none of the side topics/discussion.
Unrelated to the American Government requirement, there was an elective class titled
International Relations that examined different areas of the world and their governance by looking at one or more countries from each area as specific examples. Naturally, a such a course only focused on the key similarities and difference, but it was taught by someone who made the class as fun and informative as possible. I doubt the class would be offered in the present day, however. The portion of the class that covered the Middle East included a brief discussion on the pillars of Islam -- not to indoctrinate but to show how the area's religious beliefs had significant influence on both the laws and governance there. I can picture today's parents finding that "problematic" for whatever reason, especially since the district is now trying to add gender studies courses to the high school curriculum

.
~1/3 of Americans can't even list off a single right from the Bill of Rights and something like 2/3 can't explain how the government (state and federal) are structured, let alone why. Something like 45% can't even name all 3 branches of government.
I don't know if it's a case of not being taught, or the info just going in one ear and out the other (probably both).
It wouldn't surprise me if government classes in $CURRENT_YEAR are more watered down, cover less topics, and don't get into any sort of detail apart from what's needed to pass tests and meet the rubric established for the class. I'd also agree that there is a greater tendency for students, especially teen-aged ones, to let lecture content go in one ear and out the other for any class or content that's required and deemed uninteresting.
Coincidently also prior to this most if not all highschools, at the latest, across the country taught something called Civics.
And some of the older teachers that taught into the late 80's and beyond still called government classes "Civics" even though that might no longer be true or accurate.