The story of the OnePlus 9’s journey back to Android 11 is one of community-driven persistence against a shifting software identity . When the device launched, it was celebrated for OxygenOS 11
Why Downgrade to Android 11?
adb reboot bootloaderfastboot oem unlock (or fastboot flashing unlock); confirm on phone.Rollback Package: Download the stable Android 11 zip for your region from the OnePlus Community forums. downgrade oneplus 9 to android 11 exclusive
to the end of the APK or firmware. You must rename these files to end strictly in (for the tool) or (for the firmware) for them to be recognized. Executing the Rollback : Once the firmware package is placed in the main page of internal storage The story of the OnePlus 9’s journey back
After downgrading your OnePlus 9 device to Android 11: Setup your device : Follow the on-screen instructions