In this photo there's a beautiful cabinet with a lamp on it and artwork on the wall. Maybe you can do something like this. You'd need a carpenter to square of the top of the wall a bit for the artwork.

Waterstone Palazzo Lago · More Info

I would find out if you can drywall the right side to the same dimensions as the left. You will lose some space but it seems to be wasted space anyway due to it's strange dimensions. Then have a carpenter build built-in lower cabinets on each side, with open shelving above.

Hang neutral curtains on either side of the TV with tension rods? That room has too many focal points right now - big windows, fireplace, and these strange indents on either side of the fireplace. Making two of them fade with curtain will probably be a visual relief.

I’d put a tree there

BARBICAN APARTMENT · More Info

It depends if you want to use the space for fun or function. Here are photos to give you visual ideas:

Line narrow, tall bookcases from the back corner around the side where you currently have a shelf, but not on the side of the fireplace, as they would overlap. This would make them appear to be built-ins.

A tall pedestal table with a unique sculpture...

...or a sculpture that stands on its own.

An interesting floor lamp or mood lighting.

A tall piece of art on the wall where you currently have the shelving and use an accent lamp to highlight it.

Hope the ideas are helpful!

What’s on the other side? It’s hard to tell from the pics. Please don’t do curtains

Lol. That’s what I thought. They make bookcases for corners. You need something with a closed back to hide all the cables. Something like this might work. It’s comes in tons of colors. Just drill holes in the back for the cords

If you put big mirrors in those gaps and put a plant or two it would look like there is rich interior garden there.