For the OPPO A11K, there is to unlock the bootloader. Most custom ROM installations require an unlocked bootloader to flash a custom recovery (like TWRP).

launched with Android 9 (Pie), it supports , which theoretically allows a GSI to run on its hardware, provided a workaround for the bootloader can be found. Risks and Considerations

The gold standard for custom ROM longevity. It is incredibly lightweight, highly secure, and focuses heavily on performance optimization.