By the encyclopedia britannica:

"psychological condition defined by the English philosopher John Locke as “the perception of what passes in a man’s own mind.”

So it is impossible to prove that any being outside of oneself has conciousness, unless you compare brain scanners like they did to prove that the color blue is seen the same by everyone (same neural structures lighting up).

But... An LLM clearly can't have consciouness, as its "mind" would be the weights in the model, and the passing through it would be the data going from the input tokens to the output tokens. There is no place for the LLM to detect what is going inside and process it separately.

I don't think we need to start from definitions. You can do what we do with something like dark matter and note its observable effects, and use that to pose the problem, and ask what gives rise to those effects. You can also reason from paradigmatic examples that model the phenomena we want to explain. Or maybe heat is a better example - we didn't know what it was exactly, except for a related kludge of effects. It's something you feel, it seems related to fire, but also fevers and the body and friction and chemistry. And some amount of it turns out to all be tied together, and some amount of it gets explained away (e.g. fever and chills and spiciness aren't just excitation of molecules), but it gets explained away in a satisfactory way.

Defining consciousness would be something we're only capable of doing once we solve it rather than something to do at the beginning. I also think it "how do we define X" is a trap that sounds deeper than it is, because for some questions it gets the order of operations reversed.