Oppo does not provide an official bootloader unlock tool for the A9. You cannot simply type a command. You typically need to use unofficial, paid tools (like MTK Client , SP Flash Tool , or UnlockTool ) that exploit low-level hardware vulnerabilities. This process is not for beginners. Are There Any Dedicated Oppo A9 Custom ROMs? Here is the honest truth: There are no mainstream, stable, "one-click" custom ROMs like LineageOS or Pixel Experience officially built for the Oppo A9.
XDA Developers Forum > Oppo A9 (Codename: Oppo Realme 5 family – they share hardware) and search for "GSI Treble Guide."
The Oppo A9 (2019) was a solid mid-range contender. With its massive 5000mAh battery, a decent MediaTek Helio P70 chipset, and a sleek design, it served the everyday user well. However, as years pass, software updates from Oppo have slowed to a halt. The device is stuck on Android 9 or 10 (depending on the region) with the dated ColorOS 6 skin.
Why? Because the development community largely ignores MediaTek Oppo devices. The source code for the kernel is not fully released, making bug fixes nearly impossible.