Ubuntu doesn’t show all the start-up applications by default in its ‘Startup Applications’ manager. But you can easily display them by running a single command in terminal.
Press Ctrl+Alt+T on keyboard to open the terminal. When it opens, paste the code below and hit enter to run:
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop
Enter your user password and press ‘enter’ again if asked (note: When entering your password, the terminal will not display characters on-screen, such as the asterisk ‘*’, for security reasons).
To hide them again, run:
sudo sed -i 's/NoDisplay=false/NoDisplay=true/g' /etc/xdg/autostart/*.desktop