"Without a highlighter, I can't study" should also be accepted.
True, it is.
But it's not the most common way to say it in English.
Better get used to natural Korean word order and (most) natural English word order.
Still, you can flag it and it might get accepted eventually.
Well. If you want to say that...
형광펜 없으면 공부못해
When you switch the english, the korean will switch too depending on what you want to emphasize and obviously what feeling you want to give off.
"I don't have a highlighter so Icannot study" should be acceptable too
Why not? not the best way to translate it but still works
나는 형광펜 없(이) I don't have a highlighter (so) ,
공부를 못 해. I cannot study