"Will renting a buffer from home depot bring the shine back and get rid of the line?"

If it is in a layer of wax, probably.

It might be time for a light sanding and refinish.

Dont be fooled. If it is indeed wax. A buff and rewax will bring back the "shine" but if your scratch is in the wood. Only way to remove it is sanding. And theres no such thing as a "light" sand. Been refinishing floors for over a decade. And from a sanding perspective removing wax suckkks. But the benefits and end result are totally worth it

If it is a wax finish, you would be able to tell at the scratch.

Feel it. Dig your fingernail into it. Does it chip off? Flake off? Or does it ball up?

A drop of water in the corner, will whiten, if it is wax.

We are in the process of a kitchen reno and discovered the original 1940 pine floor beneath some layers of newer flooring materials. The rest of the house has oak HW. Since we have an older dog with thick nails and several pussycats who can think of nothing else except tearing through the house every night and riding the area rug into the living room (they all have their claws), we have been asking everyone that has come to look at the kitchen floor what to use on the oak HW to bring it back and everyone has a different answer - no wax, no buffing, one uses a Swiffer, someone else said only use Bona. We are going to look into Bona ourselves. We vacuum every day because of the pet hair and once in a while we use a Shark steam mop but that is not recommended.