The OnePlus 9 launched with OxygenOS 11, which was widely regarded as one of the most stable iterations of the software. The upgrade to Android 12 introduced significant changes:
This error often occurs when you are trying to flash a rollback package that does not match your current firmware region or when the local update APK is not properly installed. Double‑check your phone’s exact model number (Settings → About Phone) and download the rollback ZIP that matches it. Also, make sure you are using the correct local update APK for Android 12. downgrade oneplus 9 to android 11 exclusive
Likely Cause : The downgrade process encountered a critical error. Solution : You will need to use the more comprehensive MSM Tool (Method 2) to properly restore your phone. The OnePlus 9 launched with OxygenOS 11, which