Posting "trigger warning" without saying what you're warning for is a lot like saying "somewhere in this scene is a jump scare but I'm not gonna tell you where."

It entirely defeats the purpose of TW/CW/CNs.

The point of a TW/CW/CN is to tell people about upcoming content so they can make an informed decision about how to interact with it.

The key word there is "informed".

Jump scares actually are generally preceded by cues that they're coming up. Those cues (musical and otherwise) are intended to heighten the fear/anxiety experience for the audience.

You don't know where it's coming from but you know it's coming.

That's a terrible TW/CW/CN.

That's how TW/CWs without specificity work, too.

They heighten anxiety because they essentially tell you "something you might prefer to have an opportunity to consent to engage with is coming up but I'm not going to say what."

I don't think you can just have a CN on its own. I feel like if you put "content note" on something you're sort of obligated to actually say what you're noting.

Which is a benefit I'd never considered of choosing CNs over TWs and CWs.

I've been using CN instead of TW/CW for other reasons.