Itch has a native windows client like GoG or Steam to make things like library management, updates, and installs easier than just logging in periodically looking for zip files and manually putting them places. With Sophia's Secret it's a simple install button. For some reason though, I'm guessing something related to how things are published on itch, that's not an option for Claire's Nursery. It's not a client thing as everything else works fine. It just seems like there's something different that's not letting the native client understand there's a release to install.