Where are the startup/login extensions?
Access from under the apple(menu) > System Preferences… > Users & Groups > select your admin username > click the Login Items tab.
Everything there should be self explanatory.
To delete any, click the padlock and enter you username password and select the item and click the "—"(minus) box.
At least a restart may be required to prevent some deleted items from running and a Shutdown, wait 30-40 seconds, and then Startup will guarantee they won't run.
PS: Have a look at your Activity Monitor.app(Utilities folder) for some things that may start and run on their own.
Like maybe some of your "MacCleaner" stuff that you don't really need and can cause problems, but that's another subject!!!
- Patrick
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