If you own & don’t rent, I’d paint the casing of the AC unit, to match the wall.
If you rent, you could paint cardstock the wall color & tape it on.
Because the TV dominates the area, you could put another same-size picture on the left side of the TV.
I would stain both the frames to match the TV “stand”.
Add art around the TV to make a gallery wall. It makes the TV feel like part of the art wall.
I'd raise the curtains to the ceiling, perhaps extending the rod and adding one on the adjacent wall so it appears as though there's a corner window. It's very dark in this room! I would make changes to that if you own.
Add a floor lamp behind the chair. Try to find a taller light for the side table. Have you considered painting the tv stand? That would go far to updating and lightening up the space. I agree with Cheryl about painting the a/c and to put a picture the same size to the left. I would not add more dark paint/stain though! How about a bright, abstract print to again lighten the space and bring some "life" in.
Yes, either paint the AC unit the same color as the wall. You could even use removable vinyl in the same color. A large clock would be nice. Something to draw the eye seat from the AC unit but not compete with artwork on the other side of the TV. Even a floating shelves with tchotchkes (vase, trinkets) on it.
I would paint the AC unit to blend in with the wall and that's it. Then the focus is on the TV.. Sometimes we "overdecorate" just because there is blank space-----you CAN enjoy the negative space as much as an adorned one.
I would consider putting the tv and stand on wall under the AC. Cover the AC as suggested above. Put a narrow storage seat on wall that TV was on.