well it can "make choices" in the sense of having it predict a decision that someone might make. but it's not really thinking about things on it's own trying to figure it out, it's just extending the text.
For example, say you ask it: "should we ban abortion?" now, it's not actually thinking on it's own, so it'll go "what's the most likely response to this?" and give that. But if you go: "respond as a pro-life republican, should we ban abortion" the same ai model will respond "yes", but if you then go "respond as a pro-choice democrat, should we ban abortion" and it'll respond "no".
Basically it's not thinking at all, but rather just extending the text you give it (which would include a response to the question). We can try prompting it as some all knowing being, but it'll just inherently have biases depending on the exact nature of the prompting, as well as the dataset. It's not reasoning things out on it's own.
So if you ask it something it doesn't know, it'll just spit out garbage. You could try explaining the new thing in your prompt, at which point it'd respond the most likely text which may or may not be a good answer. In practice a new model would just be trained with the included topic, and it'd be the same as before: your prompt would determine the output of the ai.
Basically, it's not deciding things; it's just giving you the most likely continuation of the text. and in that sense, you can completely control the type of answers it gives. if you want the ai to be a flat earther who thinks murder is right, you can do that.