Unless you have any evidence suggesting that one or more of the variations of the Church-Turing thesis is false, this is closer to a statement of faith than science.

Basically, unless you can show humans calculating a non-Turing computable function, the notion that intelligence requires a biological system is an absolutely extraordinary claim.

If you were to argue about conscience or subjective experience or something equally woolly, you might have a stronger point, and this does not at all suggest that current-architecture LLMs will necessarily achieve it.

"Biological activity" is just computation with different energy requirements. If science rules the universe we're complex automata, and biologic machines or non-biological machines are just different combinations of atoms that are computing around.

There's a big difference between "this project is like time travel or cold fusion; it's doubtful whether the laws of physics even permit it" and "this project is like heavier-than-air flight; we know birds do it somehow, but there's no way our crude metal machines will ever match them". I'm confident which of those problems will get solved given, say, a hundred years or so, once people roll up their sleeves and get working on it.