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On macOS PlayerPrefs are stored in ~/Library/Preferences folder, in a file named unity.[company name].[product name].plist, where company and product names are the names set up in Project Settings. The same .plist file is used for both Projects run in the Editor and standalone players.
source:
Unity - Scripting API: PlayerPrefs (unity3d.com)
The folder might be hidden, check the answers to find ways to unhide it.
I can not seem to find where my playerprefs are saved on os x. - Unity Answers