I would put big, tall, bushy, fake plants in the back corners
I can put a fake plant in the right corner (my wife would like that), but do you notice the door on the left side of the second image? Well, that door stays open, so I can't put anything in the left corner. I also can't hang anything on the back wall because the sliding door is always open.
The left wall has a window at or near the first reflection point. Perhaps thick curtains will work better than the shades (?).
There's not much I can do with the front wall. Over the years, I've tried several methods to cover the TV in the middle of the speakers, but none of them improved the sound. For context, the speakers are about 4 feet from the front wall.
I hadn't really thought about it, but I can imagine the sound bouncing off those wooden walls could be a bit harsh. Except for the sofa and chair, there's nothing else in the room that's absorbing the sound. The throw rug probably isn't doing much.