I've recently installed shiny server on Ubuntu, however when I browse to the demo app it doesn't load the output properly (see image below). I've confirmed that shiny is installed and have checked the logs, but there doesn't seem to much to go on.
I have the same issue when using RStudio Shiny::runApp
That could be a a problem with your graphics device or with the permissions for user shiny.
Try installing Cairo library in your system and Cairo package in R, or uninstalling it, if you already have it installed, also make sure you have set proper permissions for user shiny.