The solution to the problem of a closed crack in the wall depends on its size and type of damage. Here are some steps that can help you deal with this problem:
Clean the area: Use a brush or vacuum cleaner to remove dust and debris from the crack.
Prepare the surface: Work the surface around the crack to remove any old paint or putty. This will help the new material adhere better to the wall.
Fill the crack: Use suitable material to fill the crack. For small cracks you can use putty, and for larger cracks you can use gypsum mixture. Make sure the material is well absorbed into the crack.
Level the surface: After the material has dried, carefully level the surface. Use sanding paper to remove excess material and create a smooth finish.
Paint or Wallpaper: If necessary, paint or go over the treated area to give the wall a cohesive look. I would recommend doing an accent wall, but which wall should be the accent wall in bedroom? I think a central wall would be ideal. As for wallpaper, you can use materials from
https://fancywalls.eu/blog/bedroom-accent-wall-ideas/, they are of high quality and easy to apply to walls.
I hope you will be able to resolve this problem as soon as possible.