So me too there are alot of incorrect solutions that wont work.
Oppo has locked the bootloader and removed fastboot acess to bootloader.
We cannot unlock the bootloader.
The only way we may be able to root this phone is with the Boot image patch method used in Magisk but Oppo also has introduced an encryption scheme to stock images called ozip. At the moment no one has been able to find a key for the oppo f9's ozip encryption.
There are a couple of python tools to decrypt ozip on github
I am not allowed to post urls yet.
None of the keys work ... I have tried to brute force by guessing random keys because i know little to nothing about encryption but no success.
Also there is a interesting git with the encryption schema itself search for ozip ecryption specks
Anyone with cracking experience might give it a go
The stock image can be downloaded from oppos support page.
Maybe we can get some support from the senior members here who have knowledge and experience.
on the specks site it is said that we can retrieve the key with :
xtract the 128-bit ECB Key (binary is here, aarch64 elf, 0x23f08)
I dont even know what that means and the link is dead.