Appropriation is stealing well.
Good stealing is obvious, fair, resonant, clever, unexpected and pointed.
Since the appropriation is part of the art it needs to be up front. Don't be obscure, or try too hard to hide the grab. Even better if it's audacious.
There is a sense of fairness amongst artists. Stealing a well known icon is okay, but to take the riff of rival, little known artist is plagiarism.
There must be a cultural or semantic resonance. Even if, as in Dada/Surrealism it's an incongruous juxtaposition. Something needs to link or amplify. Otherwise you've got a collage or mish-mash of "found" stuff that doesn't hang together, and that is considered immature.
A clever steal makes the thing you take feel like it always belonged more in your piece than the original context. That's hard, but it happens and its wonderful. Maybe you take a grab that forms the perfect cadence to an entire song you wrote, or just a sound whose harmonics make the perfect missing parts to another chord.
A completely leftfield steal borrows from a genre that is totally unexpected. There's a balance to be struck with obscurity here.
Finally, all of these combine such that an appropriation has a point. It communicates an idea, through juxtaposition, association or whatever. It references. It's a homage.
I know that the hidden question behind this post is "Does AI appropriate?"
I don't think it does, because it lacks the intentionality of the above points. But humans are great pattern matchers, including seeing patterns that are accidental, so we mat read into AI and see "appropriation" - but only in its most mechanical sense.