That is not true. We can detect the presence of a thing by the observation of something it causes. That does not imply we have a good definition of the thing.

At that point, we can only define it as something that causes this observation. And that is not very useful.

We might both agree its a poor definition, but at least it's a poor definition that's observable and neutral. That's useful in regards to this conversation.

Where as the other answer is simply "I can't say, but it's not [this]" and that isn't useful at all. It's simply opinion, which is literally the worst definition around. Personally, I don't define intelligence as "whatever qsera acknowledges as intelligence with no qualifying context"...