Login items notifications pop-up SOS

The notifications are not about the login items, per se, but about the background processes running. Those are shown in the Login Items section, but may have nothing to do with any of the actual Login Items.

Just deleting launchd plist files willy-nilly won't resolve the problem and may break the apps that you installed that are running those background processes to provide the features you installed the software to provide.

You need to figure out what installed software is running those background processes. When you do, you need to uninstall the app using the developer's uninstaller or instructions. If you need the app, you can try reinstalling and maybe it will work correctly after a reinstall. It is also possible the app developer has an updated version that works correctly.

Trying to determine which app is calling the background processes may be difficult as some are just built-in unix processes, not something custom made for the app.

The best chance of determining what you installed is by using EtreCheck. It will show you what you have installed, but won't tie any particular app to the background process.