The application I'm specifically talking about is Cisco AnyConnect VPN, which I have to use for work so I can't delete it. It opens whenever I log in and its screen covers everything for a few minutes and can't be minimized. It's really annoying and I'd like to know if there's something, maybe in its config.plist, that will prevent it from opening on startup. Does anyone know?
Yes, I'm pretty sure you can stop apps from opening on startup even though it ignores Login Items. It is most likely in LaunchDaemons.
There are two locations for these, one is for Apple daemons only:
The other is to include 3rd party processes:
You may also need to remove from:
Just remove the files of the app you don't want to launch on startup and it shouldn't show up on launch anymore.