How can we broaden our niche? Sanding plaster?

Chisel away plaster, with hammer and chisel and blue thumb (1/2 day), or with small power drill (20 min)

If it is not "very disturbing" that the furniture protrudes, I might cover the slot at the back with a well-fitted board. (the same wood or painted white) When the plaster and wallpaper are removed, this will definitely remain visible at the rear upper edge ... (no matter how much or little dust is generated) Therefore, this spot would somehow need to be "taken care of." (a - white? - quarter round rod in the corner, for example) One question remains whether it would not be easier to modify the furniture. Perhaps a side panel can be removed, the whole thing shortened, and reassembled? There is already a seam. Maybe the wall where two meet can be completely omitted? Ask a carpenter? I know situations where due to a mistake the final result is more successful than originally planned (perhaps you will be happy about a larger table surface because something fits that previously didn’t?)

I would tackle the plaster pragmatically and quickly with a multitool and accept that the wall behind the furniture no longer looks perfect. Less dirt and effort than sanding, higher accuracy than chiseling.

If we are really talking about 5 mm here (0.5 centimeters), then use a sanding block and sandpaper and sand down very carefully by hand. 5 mm is almost wallpaper and paint.

I have just gone through the same issue. Mark the edge of the wood on the wall with a pencil, then cut more precisely along the edge with the utility knife and cut more aggressively underneath. Everything below the edge is not visible. Sanding always creates dust, cutting and chiseling works well. If necessary, just run the vacuum cleaner briefly, but if you move slowly, not much will happen. But since it is probably [Gipsputz?], it can all be cut with the knife and then gently chipped away with a spatula and a hammer.

If it is only about a rear corner, then I would plane the piece of furniture at the corner. In the case of a [Hausnische], I would not even approach it for both aesthetic and practical reasons.