So how do the patron and Itch.io versions differ from each other?
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This is pretty obvious. The itch.io version is one month/two updates behind the Patreon version. And it's only updated once a month. In terms of the main game content, this is the only difference. But at different levels of support opens access to additional materials: guides on the site (for the chosen ending) and to the version of the game with a gallery (like arts from game days or music from the game)