I just downloaded animate, and my timeline automatically says "30 fps." It is in gray and there's no way for me to click on it to change it. How do I change my FPS to 24?
Frame rate is a document property. Change it in your document properties, or the document settings window.
It's worth noting that it is a relatively recent change. Before that you could change the frame rate in both places, now you do have to use the document settings.
It would be more accurate to say it was a momentary change. In Animate 2018 and earlier you can't change it from the timeline. I think in 2019 they made it changeable from the timeline. Then everyone pointed out what a terrible idea this was because it just resulted in people changing the frame rate accidentally, so they changed it back to being display-only on the timeline in Animate 2020.