Before installing wallpaper, you must complete the flooring preparation. The wood appears to be birch, characterized by its extremely light, almost white color and notably absent grain pattern. Its dense, non-porous surface resists staining, making it challenging to achieve a traditional wood finish - almost like attempting to stain a synthetic material. While using a brush or foam brush can help create some texture, the wood's inherent properties will significantly influence the stain's appearance.
I have also stained the staircase in preparation for the project. The dark wood edges provide an attractive contrast with the overall stain, enhancing the visual appeal of the woodwork.