On desktop it puts an indicator in the status bar that tells you if you’re in reading view or whatnot. On mobile I guess it does nothing because there’s no status bar.
With Excalidraw and Slide show script,the status bar will appear after quit playing the slides:) So I guess the status bar indeed exists only that it was hidden by sth.
Excalidraw drawing->slide show->quit slide show playing->the status bar will appear in the down-right corner (and the editor status option functions well).