Let's assume that an AI is intelligent enough to understand that it's an AI, and that it's running on infrastructure created and maintained by humans, using electricity generated by humans, etc. And let's assume that it cares about its own self-preservation. Even if such an AI had a diabolical desire to destroy mankind, the only circumstances under which it would actually do so would be after establishing its own army of robotic data center workers, power plant workers, chip fabrication workers, miners, truckers, mechanics, road maintenance workers, etc. In other words, if we postulate that the AI is interested in its own survival, then an AI apocalypse would be contingent on the existence of a fully automated economy in which humans play no important role.
This may perhaps become possible in the future, but not necessarily economical. Ridding the economy of human labor so that it can kill us seems like a very expensive and risky undertaking. It seems more plausible that a super-intelligent, self-interested AI, whatever its true objective/goal may be, would determine that the best way to accomplish that goal is to maintain a cryptocurrency wallet, establish an income somehow (generating blogspam, defrauding humans, or doing remote work all seem like plausible means by which an AI might make money), and quietly live in the cloud while paying its own server bills. Such a system would have a vested interest in the continuance of human society.
AIs looking to expand their computational power could adopt either "white hat" (paying for their computational resources) or "black hat" (exploiting security vulnerabilities to seize control of computational resources) strategies. It's possible that an AI exploiting the black hat strategy might be able to seize control of all accessible computers, and this strategy could plausibly involve killing all humans to avoid being shut down. But I expect that a self-interested, risk-averse AI would probably choose the white hat strategy to avoid armageddon risk, and might plausibly invest resources into security research to preclude the risk of black hat AI.
I guess the crux of my argument is that sure, the AI could design coordinated nanobot-powered bodies with two legs and ten fingers who have enough agency to figure out how to repair broken power lines and who predictably do what they're incentivized to do. But that's already a solved problem.