If your device never received the OTA notification, you are not alone. Most F3 units remain on Android 7.1.1 (Nougat) or Android 6.0 (Marshmallow) by default today.
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If you are looking to update your OPPO F3, you are generally limited to the following official and unofficial methods: OPPO F3 (Diwali Edition Red, 64GB) with Offers - Amazon.in If your device never received the OTA notification,