(I only wanted to comment but am still too puny for that.)
No. As @transitionsynthesis says, LLMs do not come in contact with Wittgenstein and so can't support or refute him. Meaning (and Wittgenstein's "use") requires intention, which LLMs do not have. Strictly speaking they are only pattern-matching systems and don't even have anything to do with language -- language only happens to be the medium in which they match patterns. If their responses to our prompts seem meaningful to us that's a coincidence -- a hallucination on our part -- and the meaning we find is our use of the words, which involves the intention of our reception ("How can I apply this string of terms to my question about good ways to melt an egg?"). You might take that as support of Wittgenstein's proposition, but it has nothing to do with the LLMs -- it's the same use we make of all utterances we receive.
So, frame challenge: I think OP's consideration of LLMs in the question is an error. The last clause, "Is 'meaning' really just use?" is a good question. But since the speaker (or anyway, word-emitter) in the situation is an intentionless automaton the only "use" involved is that of the receiver. That being the case, the fact that this producer is an LLM is irrelevant -- the source might be ChatGPT or words drawn from a hat or a Magic 8-Ball.
So the success of LLMs at producing word-strings to which interpretations can be applied neither supports nor refutes the idea that "meaning is use". With respect to that proposition we're left in the same position we've always been in when considering "meaning" from only the recipient's point of view.