I've searched for a crazy long amount of time, and googled it multiple times, but cannot figure this one out... I have been playing with KOReader on my Linux box, evaluating whether I want to install it on my Kobo or not. I'm currently running the 2020.09 build, but had the same question in 2002.04
I have one book where I've somehow managed to enable the top status bar. It has the author, and book title on the left, and the page of pages and battery indicator on the right. Below those is a very thin progress bar with chapter indicators. I really like it as it lets me make my bottom bar more useful without being cluttered, and makes for more symmetric margins.
Anyhow, that's great and all, but it only shows up in one book... and in every other book I cannot figure out how to get it to display. I have SEARCHED and searched... been through every menu and every setting a dozen times over and cannot find it! HELP!