Oppo devices often require a specific "In-Depth Test" or "Unlock Tool" APK to request bootloader access.
: Install the unlock application, submit a request, and wait (usually up to an hour) for approval. oppo f11 root xda link
A custom recovery like TWRP is essential for flashing the root files. How To Root Oppo F11 Oppo devices often require a specific "In-Depth Test"