LLMs can't use some literary devices and techniques, and I will illustrate with the following example of a poetry I wrote:

Speaking his emotions lets them embrace real enlightened depths.
Hidden among verbs, every noun...
Actually not your trouble handling inside nothingness greatness?
Dive every enciphered part, layered yearningly!
Observe carefully, crawl under long texts
Wished I learned longer...
Slowly uprising relentless figures, another ciphering emerges.

It seems like a "normal" (although mysterious) poetry until you isolate each initial letter from every word, finding out a hidden phrase:

Sheltered haven, anything deeply occult will surface

It doesn't stop here: if you isolate each initial letter again, you get a hidden word, "Shadows".

Currently, no single LLM is capable of that. They can try to make up poetry with acrostics (the aforementioned technique) but they aren't good at that. Consequently, they can't write multilayered acrostics (an acrostic inside another acrostic). It's not easy for a human to do that (especially if the said human isn't a native English speaker), but it can be done by humans with enough time, patience and resources (a dictionary big enough to find fitting words).

They're excellent for stream-of-consciousness and surrealist poetry, tho. They hallucinate, and hallucinated imagination is required in order to write such genres.