In my case I don't remember the book well enough to remember most of it. I read* it more than half my lifetime ago in English class as a teenager, in a country that wasn't the US, without access to the dispersion of ideas (the 90s Internet was much less discoverable) we have today.
I remember Scout in the early chapters far more than I remember Atticus because I too was broadly speaking a tomboy and thought of myself as smarter than my teachers. I identified with her. I imagine the whole "smarter than teacher" thing struck a lot of kids more than the big important message.
However, I do still remember the jail scene and the gist of the closing arguments from Atticus. Around the same time, I saw A Time to Kill (I think at home on tv) and remember the closing arguments in that. And at some point, I think in history class, we also studied Mississippi Burning.
These three things specifically stick in my mind when I think of race in the US^, and influence me even today. So perhaps the book did get lost to the movie version for some people, but as a non-US kid in the 90s, I think a lot of it went over my head.
I think I'm going to go back and read it again.
* I'm pretty sure I didn't Cliffs Notes this one, but I can't remember for sure. I don't remember seeing the movie, we might not have.
^ I don't think we ever really got introduced to the other racisms that the US has, eg Hibernophobia (irish), Italophobia, anti-semitism, etc, but I did learn about these from TV