Help please!

Honestly I wouldn't jam it up too much with stuff as it's the main traffic pattern to the dining room. Do the double doors lead to a bedroom? I think you could do some kind of wall unit. Some open sections for books and knick-kicks and closed sections for extra storage. I would put a shallow unit on the wall with the Beachwalk art because the counter already juts out there. Maybe 12-13" deep. adjust wood artwork to be centered in new space.

Maybe a trio of floor vases.

Can't tell what is going on. Take better pics. In daylight, from the doors behind, and add more angles as well.

You don't need anything behind that sofa. It's an open, airy passageway to your dining area Moreover, your conversational area is pretty small and a bit crowded so having some airiness behind the sofa works very well.

Here's an article about the importance of "negative space." https://www.houzz.com/magazine/the-power-of-negative-space-in-interior-design-stsetivw-vs~97343035

Maybe tweaking other parts of the room will help pull the space together--sofa pillows that echo your green wall with a bit of blue that links to the blue in your art:

Plutus Bear Canyon Handmade Throw Pillow, Single Sided, 26x26 · More Info

Possibly consider a patterned rug that contrasts better with your floors and also references your green wall:

Surya Aura Silk 21724 Machine Made 2' x 3' Area Rug in Lime, Dark Green · More Info

Do hang your dining art work a bit lower. The center of the art should be about 57" from the floor.

Don’t just add something to fill up space. You may come to realize you NEED a piece of furniture or a storage cabinet for a particular purpose.
Do you need better lighting near the sofa? If you add a sofa table or a console behind the sofa, is there an outlet in the floor to plug in a table or floor lamp?
Do you need a storage piece for photo albums, craft supplies, occasional-use serving dishes or gift-wrapping supplies?

A beautiful rug as suggested by housegal200 would add color, pattern and texture. (A rug laid on a wood floor may need a thin rug mat to keep it from sliding.)

I'm thinking more about filling up the corner rather than behind the couch. Idk why it just seems so empty to me.

It would be a great spot for a desk, bookshelf or storage piece.

I agree this looks empty but space can be tricky in pics. How large is the space? Can you share a floor plan with measurements? What's behind the French doors? Do they open out of this room?

How can I open up the furniture in the middle? Thanks.

Please provide additional photos from all four sides of the living room area, especially the wall opposite the sofa. As I suggested, you need some breathing space, and you have it, in that corner and the sofa. Let's see your living area from other angles to see how it can open up.

In the future, always include photos of all sides of a room, the dimensions, what absolutely has to stay, how you use the space. You'll get more and better responses when Commentors can evaluate the whole space.

Cant really tell exactly how much space you have there without dimensions, But here are some ideas ; an ottoman/ storage bench if you need seating.

Or a slim console which had a depth of 10"-12". If you are considering this one though, the artwork you have on that wall will need to be moved a bit higher.