Now this may be a stupid question maybe just an update, but it could also be that nitrogen for some reason isn't aware of me having two displays since the option I'm missing seems to be the one where to select which screen a wallpaper goes on. I was trying to follow this answer. Image of my nitrogen window
would you be open to a more modern (and more akin to 18.04/19.04) solution ?
if so then run (this will reboot your system when it's done) :
sudo apt-add-repository ppa:alexlarsson/flatpak -y && sudo apt update && sudo apt install gnome-software-plugin-flatpak -y && sudo flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo && sudo reboot
then open up the software center and type "HydraPaper" and install what comes up.
then you may run HydraPaper and :
the "Dec '13'13" in that rectangle translates to "the 13th of december in 2013"
the user states he is using ubuntu 13.04 right after his diagram.