For those who are wondering about the "Crash after unlocking a category" problem mentioned below by some members, know that it is most likely due to a bug in the game code that requires the dev to fix. For more details and possibly future updates, please see here~! 🙂
Indeed, as soon as you satisfy the unlock condition for any of the unlockable categories (except [?]), game crashes and can't launch again. Going into the save file and manually deleting the last completion record from there (of the puzzle completing which would unlock a category but crashed the game) allows the game to open again. But you can never complete that last puzzle which would unlock a category, and therefore no additional categories are available (except [?]).
For those who are wondering about the "Crash after unlocking a category" problem mentioned below by some members, know that it is most likely due to a bug in the game code that requires the dev to fix. For more details and possibly future updates, please see here~!
🙂