"an LLM" could imply an LLM of any size, for sufficiently small or focused training sets an LLM may not be transformative. There is some scale at which the volume and diversity of training data and intricacy of abstraction moves away from something you could reasonably consider solely memorization - there's a separate issue of reproduction though.
"novel" here depends on what you mean. Could an LLM produce output that is unique that both it and no one else has seen before, possibly yes. Could that output have perceived or emotional value to people, sure. Related challenge: Is a random encryption key generated by a csprng novel?
In the case of the US copyright office, if there wasn't sufficient human involvement in the production then the output is not copyrightable and how "novel" it is does not matter - but that doesn't necessarily impact a prior production by a human that is (whether a copy or not). Novel also only matters in a subset of the many fractured areas of copyright laws affecting the space of this form of digital replication. The copyright office wrote: https://www.copyright.gov/ai/Copyright-and-Artificial-Intell....
Where I imagine this approximately ends up is some set of tests that are oriented around how relevant to the whole the "copy" is, that is, it may not matter whether the method of production involved "copying", but may more matter if the whole works in which it is included are at large a copy, or, if the area contested as a copy, if it could be replaced with something novel, and it is a small enough piece of the whole, then it may not be able to meet some bar of material value to the whole to be relevant - that there is no harmful infringement, or similarly could cross into some notion of fair use.
I don't see much sanity in a world where small snippets become an issue.
I think if models were regularly producing thousands of tokens of exactly duplicate content that's probably an issue.
I've not seen evidence of the latter outside of research that very deliberately performs active search for high probability cases (such as building suffix tree indices over training sets then searching for outputs based on guidance from the index). That's very different from arbitrary work prompts doing the same, and the models have various defensive trainings and wrappings attempting to further minimize reproductive behavior. On the one hand you have research metrics like 3.6 bits per parameter of recoverable input, on the other hand that represents a very small slice of the training set, and many such reproductions requiring strongly crafted and long prompts - meaning that for arbitrary real world interaction the chance of large scale overlap is small.