If you could hang artwork over that electric panel it would add color and hide the panel. Or hinge it on one side. Or use a mirror. Or just a canvas over a box frame.

I agree a runner would add some warmth but still allow some modernity. You have a totally blank canvas right now (which is great!) so maybe start with deciding if you have any preferred colours you would like to work with, then you can add a runner, art. As for covering the electrical panel you would need to check in if there are issues with that - in an emergency someone may need access and to be able to find it easily (even if you are not there) and depending on your locality covering it may be an issue.

I think that the wall space on the immediate left of the front door for art and a runner would be the perfect combo to brighten your space. You don't need a lot, but something colorful or dramatic would be wonderful. Let me find something that works.

Here is an insp pic for you to get started.

A couple of more below:

Are you against painting the walls and/or interior of front door?

Hello
everyone! I really appreciate all your comments, photos and suggestions. Painting
the door would be difficult, but the walls is ok. I have a couple of questions
concerning this point: Could I paint only the corridor and keep the walls of
the other rooms (living and dining room) white? What colors would go well?

I have a big problem with the
combination of colors and materials, that's why I always choose white, black or
gray. However, I'm tired of that and that's why I'm looking for help. Don’t
think that I have not tried, but I’m not good on that. I share with you a couple
of photos of the staircase and the living room. Hope you can help to choose the
right color in the wall and the runner to get a cousy and modern ambiance.

The glimpse we have of your living space shows that you have a great sense of design. But are you afraid of color??? I would keep your walls white. But pump up the energy with some color. I love Danita’s last example of colorful art and a vibrant runner. You can then use a color from the artwork inside your living room as a throw or pillow on your beautiful couch to draw your guests into that space from the foyer. And that color can change when you like with minimal expense. A lovely space!

Hello everyone, thank you
so much all of you for your comments, photos and suggestions. I’ll take them into
account. “See” you soon with more questions J

Painting the inside of the front door black would add some fun drama to the space.

Why not try a runner and a piece of art over your white table? We will include a few of our designs to aid you with your dilemma.

Dear Betty, thank you so much for your advices and photos, I loved them. One last question, the piece of art with blue, could it combine well with the stairs and the the living room? I send you other photos. Thank you in advance for your comments and suggestions.