Objective-C, as I explained on FB the other night, is mostly for legacy code. Even at Apple, unless you're directly working with macOS, you're probably unlikely to ever use it there since they're clearly transitioning to Swift now.
I personally know Objective-C better since when I started iOS development, all the tutorials were in that language since Swift was way too young at the time. And I'm glad I did.
While you could use Xamarin these days, the downside is it's still a young Microsoft tool.
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