Dumdum An example would be KDEConnect which, unless I'm missing something, can't be prevented from running short of simply disabling the entire app from app settings.
At present I suspect you have two options, namely disabling the app or putting it in a profile that you stop. I think the issue is that some apps that declare they need to run at boot really do need to, e.g., any keyboard used to unlock the device. So adding a toggle to disable launching at boot would not just be work, but it might also get a lot of people into trouble.
I wonder if the KDEConneft authors would be willing to add a setting for not running all the time?