As i am a old guy i read mostly on big screens,not on the mobile much,if i am, using a 15" screen and the standard pi case. And now calibre 8.4.
Using X-11 and install libxcb-cursor0 then Installing and updating using the standard " sudo -v && wget -nv -O-
https://download.calibre-ebook.com/linux-installer.sh | sudo sh /dev/stdin"