> We know this is only 200,000 neurons. Dogs have 500 million. Humans have billions. But where is the line for sentience, awareness?

Check out the venerable fruit fly (drosophila melanogaster) and its known lifecycle and behavioral traits. They're a high profile neuroscience research target for them I believe; their connectome being fully mapped made the news pretty hard a few years ago.

Fruit flies have ~140,000 neurons.

The catch is that these brain-on-a-substrate organoids are nothing like actual structured, developed brains. They're more like randomly wired-together transistors than a proper circuit, to use an analogy.

So even though by the numbers they'd definitely have the potential to be your nightmare fuel, I'd be surprised if they're anywhere close in actuality.