You don't need to give permission on installation.
When you installed Pokémon app, go to security, then permissions, find app and give location permission.
Next go to app battery saver, find app and put "No restriction" and allow "background location".
Aditional tip, if you wish to Pokémon work without issue you'll need to put in Location settings "high accuracy". Also avoid using Miui batery saver features, it will do more harn then good while playing Pokémon go, you get faster high temperature.
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