Among the many feasible vectors you could accomplish that: Bitmain’s HQ is in Beijing, and while there is some scrutiny on the subject there has never been a (public) investigation into what’s actually baked into the silicon. Antminers are a fucking stunning percentage of the nodes out there, and although nothing like 51% of all nodes are just antminers, it still wouldn’t be difficult (for a powerful nation-state) to repeat the process across multiple manufacturers and get that kind of distributed influence.

It’s completely possible that the classically imagined 51% attack has never occurred, but having that kind of large influence over the blockchain would trivially allow for subtle manipulations that would have world-spanning impacts. We have no way of demonstrating that it’s happened, nor preventing it if it does, which is a big part of why bitcoin is regarded as such a joke by everyone that isn’t part of the cult. And to be clear, I have no idea if this has happened - that’s the problem, there’s by design no way of checking or verifying integrity on that scale.

Bitcoin was a half-baked idea that’s only stuck around because of the speculative market.