You'd have much better retention rates if you don't cover up the content the viewer is trying to view.
How would you like it if I shoved a banner in your face the moment you walked into a store and forced you to punch a hole in it in order to view items on the shelves?
So uh, don't do that.
You don't need to notify if you use cookies for required functionality like login sessions or remembering a functional setting.
If you're tracking whether they're returning or not your activity is exactly the kind of behaviour the rule is covering because, in legal terms, it's skeezy as fuck.
Nobody wants to be the EU test case on precisely how "required functionality" is defined. Regardless of what the plaintext of the law says, it should be self-evident that companies will be more conservative than that, especially when the cost is as low as adding one cooke banner and tracking one preference.