You can disable startup apps in Ubuntu with Startup Applications. By default, some bloatware is hidden on Startup Applications on Ubuntu. But this never means they are unsafe to disable from startup applications list. Lets unhide default startup applications from Ubuntu.
1- Open Terminal.
2- Paste this command to there:
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g' /etc/xdg/autostart/*.desktop
Now you will see something like this on "Startup Applications".