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.
I would think that qualia is the element of that list that actually matters here- "Is there a way that it feels to be an LLM?" is, I expect, the underlying question being asked within "Is an LLM conscious?". If LLMs could only experience the timeless, nonlocalized color blue, they'd still be conscious. The presence of positive and negative valence qualia is additionally relevant if someone is getting at whether they have moral worth, but it's secondary.
But qualia are not directly measurable and the rest of the list only matters if those features are necessary for qualia, which we can't decide without such measurements or at least a strong theoretical model.