To install apps from an unknown source please follow below the path:
Setting method:
realme UI 3.0 & above versions: Settings > Search "Installation sources" in the search bar > turn on the corresponding application switch to install the app.
realme UI 1.0 & 2.0: Settings > Security > Unknown source installations > turn on the corresponding application switch to install the app
realme UI R & Go & T & S Edition: Settings > Search "Install unknown apps" in the search bar > Install unknown apps > turn on the corresponding application switch to install the app.
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Unable to install the app after downloading