It depends. Instagram may notify the creator in some cases. But if their notification settings for story screenshots are turned off, then they won't know. So, it's not always possible to be sure they won't find out.
Technically, you can screenshot an IG story, but whether the creator knows or not is tricky. Instagram used to always notify the creator, but now it's up to their individual settings. So, if they have not enabled the screenshot notification, you might be able to screenshot without them being aware. However, it's still important to respect people's privacy and the content they post.
There's no guaranteed way to screenshot an IG story without the creator knowing. Instagram has features that can notify the creator when someone screenshots their story. Some people may disable this notification, but you can't be certain. Also, even if they don't get a direct notification, they might notice if their story is shared widely and suspect that screenshots were taken. So, it's always best to ask for permission if you're unsure.