Where can I find the startup application list in a Cinnamon + Ubuntu desktop?
cinnamon vs gnome
Cinnamon inherits many of its features from Gnome itself. Thus in most cases, you can use the gnome functionality to achieve capabilities that are not explicitly wrapped up in the main Cinnamon desktop.
In this case you can use
but there is an applet for that...
There are many applets available that wrap just this functionality for you.
Extracting this applet to
It should be listed under Preferences. Alternatively, just write startup applications in the search box.