Once you’re in reader mode, you have to click to get to another page, and then, if you want reader mode, you have to click again to turn it back on. Maybe make the other nav links a tiny bit less hidden and let them work and leave it on when we get to the next topic.
Another idea, turn it off automatically when you get to the end of the topic.
Or, automatically navigate to the next topic in the last topic-list you visited!