I follow… this is an interesting one @j.jaffeux and one that is incredibly hard to workaround.
To work around this issue we would somehow have to scroll the entire view and keep the composer overlayed on top of the content. Its a radical change to how we are positioning stuff and we had to work very hard to get stuff to behave properly on iPads and iPhones.
Thanks for raising it @volanar, I am just not sure there is any easy fix here. The workaround of using a PWA or DiscourseHub is the only one I can think of in the very near future.