You are completely incorrect. You're falling in the same trap that most humans fall into. That is you're completely incapable of seeing intelligence at different scales.
Cells have intelligence. Organs have intelligence. Bodies outside the brain have intelligence. Hell, many scientists accept that things like proteins likely have intelligence as they can adapt in their environment, and many more are making claims that algorithms have intelligence.
You, as of so far have given no explanatory evidence of where intelligence emerges from, only "I'll know it when I see it". The actual definition of intelligence doesn't work this way. Any, and I mean any neural network is capable of narrow intelligence. Going lower into algorithmic intelligence, the applications and CPU on your computer are intelligent in some measures.
Go outside of your extremely narrow definition of whatever you think intelligence is and learn more about it. You could start studying now and it will take the rest of your life learning more to grasp how far the scales of, the simplicity, and the complexity of intelligence actually go.
I think we need to start by asking a better question and not try to simplify too much. We also need to accept that some answers are complex and not everything can be reduced to a soundbite to be used to end internet discussions.
Let’s take a different question, like “what’s missing from a worm for it to be able to fly”. We might be drawn to the simple answer of “wings” but that isn’t quite right—ostriches and penguins have wings and they don’t fly, so obviously there are other variables at play.
How about “what’s missing from a spec of dust for it to be intelligent”. Well, there isn’t one thing missing and there’s no simple thing we can just add to make a spec of dust intelligent and sentient, its very nature needs to be radically different.
What test would you propose where an LLM (or an RL agent containing an LLM) would reliably fail, but where an average human would reliably succeed?