Setting LSApplicationCategoryType

Is this a valid thing to include in the Info.plist file?

That depends on the context. If you’re submitting a macOS app to the App Store then LSApplicationCategoryType is required. In other contexts, it doesn’t make much sense, although it probably won’t cause any harm.

If so is a category of public.app-category.astronomyvalid?

No. The valid values are listed in the docs.

My general advice on this front is that you look at the categories used by other popular apps in your space and choose one based on that.

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—
Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@" + "apple.com"

That's a pretty useless bunch of categories (unless you write games) - mine fits pretty much none of them - it fits astronomy and astrophotography, but not much else and neither are in there.

Ho-hum, So ist das leben!

Thanks, David