To the best of my knowledge, there is not an agreed and actionable definition of consciousness, and any attempt to make one comfortably fails to cleanly divide humans from machines.

It's more of a vibey term, and as such it is genuinely very difficult (perhaps impossible even) to concretely determine whether an LLM possesses consciousness. LLMs successfully express a lot of consciousness-like traits.

At some point you have to ask the question: does it even matter? If an LLM can sufficiently mimic consciousness, isn't that sufficient for us to treat it as conscious, even if it is in-fact not conscious (especially because we don't actually know)?