This feature was exclusively part of a joke version and is not currently planned for addition to regular Minecraft. It is documented here on the wiki due to being officially-released content by Mojang Studios, even if not present in a final version.
This block is available in the creative inventory, and naturally generate in the "missing" dimension. It is also seen in other dimensions, one of which is the "gallery" dimension, although it is difficult to find the stairs hidden among thousands of other blocks.
Breaking[]
This block requires a diamond or netherite pickaxe to mine. If it is mined with anything else, it drops nothing.
Natural generation[]
This block naturally generates in the "missing" dimension as the stairs leading up to the chest containing the footprints. 7 stairs generate here.