Why "login items" notifications pop up while there's no app listed on startup or background?

Jay Gamel wrote:

... What I would like to know is why apple cannot identify the offending app and include it in the notice. Obviously, the warnings are issued on a specific instance related to a specific app.

You're right, but identifying the app in question can become very challenging, particularly for apps that a user installed under the guise of something "free" — for example, products specifically designed to harvest personal information and / or deliver targeted interest-based advertisements that accrue revenue simply by loading a webpage.

People have been plucking that poison fruit for years, but the creeping incremental nature of such things appears to have motivated Apple to finally Do something!!!™ exactly as users have been clamoring for them to do, and for at least that long.

Well, guess what? They got what they asked for. Apple's implementation of it is imperfect, but if I had a better idea I'd be sure to recommend it. Or, I'd develop it myself.

Which brings us to:

I am not a programmer so I don't understand what prevents the app ID from being recorded and reported.

Mac users are not expected to be programmers. They aren't even expected to know much about computers or anything else of a technical nature. They just want to use their magical Apple stuff and not have it get in the way of doing whatever it is they need them for.

So, what about inexplicable annoyances regarding mysterious login items, or intrusive dialogs like "<suspicious_app> may damage your Mac" that result as a consequence of a Mac user installing something they may have long since forgotten about?

Fortunately, some of us are programmers and are very good at it. EtreCheck can help identify what those apps may be, and will help others suggest what to examine and / or delete at the user's discretion. To learn how to use it and how to post its report in a reply to this Discussion or any other, please read How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report - Apple Community.

By the way I have not read all nine pages of this Discussion. If EtreCheck was recommended elsewhere I wouldn't know. When a Discussion gets this long and convoluted few people will be sufficiently motivated to study it in any depth, so if it was already suggested it's probably a good idea to reiterate it anyway.