Thank you for your help Ulli
I also fail to activate the hidden column mode it switches to the corresponding reflow, like krish, or if clicked a little higher, just quits the zoom menu. I also have firmware 15.2, downloaded from the German website (however, I always have the word "reflow" displayed as in my screenshot).
May I ask you what firmware version you have, Ulli?
Also, I remember reviews of the pocketbook mentioning explicit column mode, and the features list of all pocketbook devices include that on the wiki. Is it possible that this feature was removed by some firmware update?