She's not really doing nothing, at this stage their brains are stimulated and developing so much even just while they're lying there looking at their own hands or thinking about things they can see and feel. I wouldn't worry about it at all, it's also great that she can be awake and chill without needing any kind of stimulus - if she can get used to that it bodes well for when you want to do things like travel or go out for a meal 😊
My baby (9 weeks) does this all the time, it creeps me out 🤣 unless I'm trying to get chores etc done, I tend to pick her up and hold her instead because I feel bad haha. Don't want her to feel like I've just abandoned her. Even if she doesn't seem to mind🤣