I've played a number of Ren`py novels on android.
A few have a back button for scrollback, some, like yours, have a scrollback option by tapping the left or right side of the novel… however it doesn't function during choices for any of them… like… I'll be given choices, and get distracted by being asked a question, and then forget what it was I'm supposed to be answering "agree\disagree", "hand it over\keep it\tear it", etcetera, to, and if I forgot to save recently I lose a lot of progress; because while I can right-click on PC to open the save screen, I can't on Android and all the buttons at the bottom of the screen are gone during choices… And then there are a few that just straight up don't have a scrollback feature at all.
A few Ren`py novels solved the text input issues by having the dialogue and input boxes at the top. For all Ren`py novels, though, if default input text exists, it's a huge hassle to clear, since for some reason, Android doesn't like backspacing default text in Ren`py… No idea why…
And you're quite welcome.