The Oppo F3 was released in 2017 with Android 6.0 (Marshmallow) out of the box. In 2018, Oppo started rolling out the Android 7.1 (Nougat) update for the device.

A completely barebones Android experience focusing purely on speed, battery longevity, and lightweight operation. Prerequisites Before Flashing Nougat via XDA

This is required to modify system partitions.

This allows you to "flash" files that the official Oppo recovery would reject.