I think you can reliably assert that X != Y without having a complete definition of Y, as long as you can identify at least one property or condition that Y possesses which X violates.

So for consciousness and LLMs it could be Qualia, lack of semantic understanding, lack of continuity in time, lack of a high degree of integrated causal feedback, etc.

Or perhaps those are just features of human consciousness but not integral to consciousness as a whole. To me this then implies panpsychism to some degree, which I'm alright with too.