a house that was built right in the middle of the anthracite era, light to dark gray as far as the eye can see. Nevertheless, I like your couch, rug, and some of the decorations.
Jasmin has certainly tried 100 times to arrange the couch as shown in the ground floor plan, that is not the solution.
What stands out, as in every one of these identical houses, are the bare white walls in the "hall," the result of the typical open-plan space and lots of windows, as everyone wishes. The days when a living room wall was completely covered with a wall unit are over, and now people complain about the "nakedness" of the room they absolutely wanted because everyone else has it.
Here is an example of what you can do to at least give the room a focal point.

imagine the Christmas decorations removed, unfortunately I couldn't find a picture without them. The room is about 275-280 cm high, the entrance is on the right. The room is equally deep again; where the picture was taken, there are 2 armchairs positioned at a right angle to the couch.
What can be done relatively easily and has also been done here is to install floating shelves with lighting. In the middle, you can build a "fireplace" with drywall, about 40 cm deep. Whether you install a fake fire at the bottom or not doesn't really matter. Where the picture is hanging here, a TV could also hang.
On the right and left under the shelves, for example Besta furniture.
What makes it cozy here, however, are the ceiling moldings (is that what it's called in German?) and baseboards.
Unfortunately, your floor tiles emit not a hint of coziness; I would cover them extensively, but not also in gray.
As others have already written, Artemis lights would help. In the shown room, there are two small ones, in the other living room at the other end of the house two large ones with the arch.
In another room, unfortunately also with Christmas decorations, it looks similar but without a fireplace, only a TV in the middle

the glowing line is part of a Flos light above the dining table.