You can't use 'undaunted' in this context. 'Fearless' would be better'.
You are only 'undaunted' concerning a specific situation. It means 'not daunted by' - i.e. there has to be something to be daunted by, in order for you not to be daunted by it.
Also, it'd be more natural to write 'less daunted' than 'more undaunted'; so I think that's another reason this sounds so unnatural. But in general, you wouldn't use daunted/undaunted in this context.
Why is "Đứa trẻ muốn trở thành không gian góc" refused ?
Because it isn't using a comparative.
Sorry my bad, I wanted to ask for "Đứa trẻ muốn trở thành gian góc hơn." and lately I was told by someone the difference between trở thành and trở nên. I found the explanation here