What's the point of a desk surface you can't write on? I see what it is and the message but in the end function matters. I agree the chair has to go. I would look for a light carpet to dispel the darkness a bit.

It will be tricky about what size rug you select and how you place it. Normally I would NOT place the rug under the desk chair. The location get too much wear and tear and shows signs of soiling immediately.

Select a light colored contemporary pattern rug for this location.

Which chair are you suggesting we ignore - the one behind the desk or the upholstered one to the right?

If you’re keeping the chair on the right, I agree that you should find a light colored rug to blend with it. And also agree that the rug have a pattern to disguise wear.

I agree that a lighter rug would help balance the dark walls and wood without competing with the silver desk. I’d go with a light beige, warm gray, or muted taupe rug with a subtle geometric or textured pattern. A pattern would also be practical for hiding everyday wear. I’d keep the rug large enough to define the seating/work area but avoid putting the main chair completely on top of it if that creates too much wear.