Took me a long time to get this sorted on android. Stackoverflow is full of I guess old articles saying the facebook uri is like fb://profile/username or fb://page/username. But it doesn't work, just loads the facebook app to the default your profile view.
I guess as of a certain version it is required to load into a special child view or something, anyway, this is the code that works.
Was super straight forward on iOS, just fb://profile?id=username
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