Worse-case scenario, AI finds a way to mine Bitcoin on its own and manages to control a sizeable portion of the network's hashrate (raising the risk of a 51% attack). But this is very unlikely to happen anytime soon. Bitcoin is an open source cryptocurrency, so it'll be easy to tweak it against AI threats. With a community-approved hard fork (or soft fork), Bitcoin will remain as secure and reliable as usual. Not even Quantum computers stand a chance against Bitcoin.
That's not how AI work. AI cannot magically produce compute capabilities, or have the ability to mine Bitcoins, or do anything of that sorts. AI, as of now is very much misunderstood, and they are not like the Terminator movies. AI (or rather LLM as you know it), are designed on a huge corpus and are just fancy math. There is no chance that would take, over the world, or something.
While it may not be able to do it with Bitcoin (since it's way beyond gpu miners), it "can" do with gpu mining ones, which means, AI uses gpu mainly and nvidia as well. So if AI companies like openAI, realizes a way to make chatgpt smarter, and figure out a way to mine at a much higher hashrate than what they normally would, and use their gpu power to do it, they can take over any coin that is possible to be mined.
Fortunately, most of them are gone now, there are few strong gpu mined projects left, most either switched to some other way, or they are just centralized and already mined shit stuff anyways. Aside from that, I do not see how AI could take over bitcoin, doesn't really look like it would be a possibility.