Stick with the stock ColorOS (debloat via ADB if needed). If you want custom ROMs, consider switching to a device with better developer support (Poco, Xiaomi, OnePlus).
: Backup all data as this process will wipe your device. oppo a11k custom rom link
Access features from Android 11, 12, or even 13 that may never officially arrive for the A11k. Stick with the stock ColorOS (debloat via ADB if needed)
This is the only "true" way to get AOSP (Stock Android) on this device. You would flash a generic system image (like Phh-Treble or AOSP 10/11). oppo a11k custom rom link