Most of them use Live2D (or other alternatives, some even use adobe), so they're manually animated.
Others do use AI, but the result isn't as good imho. Those who do either run their models (require big GPU) or rent/use it on a website like Civitai, either way, money is involved.
If you're interested in the type of AI they use, I seem to recall it was called "wan 2.1" but I might be misremembering here.
There's also veo3, but that's good for SFW.