My world option to play doesn't show. I have a world but the option to play it wasn't there. But when I check in the storage in the setting, I have founded my world there, I recognised it by the image (world_icon.jpeg), and it's now called “unlisted world”.
In summary, I can't play because my world is unlisted.
The tag in level.dat responsible for this seems to be HasUncompleteWorldFileOnDisk. When set, the world is unlisted.
The Fix:
The player should be able to attempt recovery of a save by an in-game GUI added to the game by simply setting HasUncompleteWorldFileOnDisk to 0. The world may show up once more.