Path A — Official local rollback (recommended if OnePlus provides an official rollback package for your build):
To downgrade your OnePlus 9 device to Android 11, follow these steps: downgrade oneplus 9 to android 11 exclusive
# Enable OEM unlocking in Developer Options adb reboot bootloader fastboot oem unlock # Accept on device screen Path A — Official local rollback (recommended if
you downloaded. You may need to enable "Install from Unknown Sources" in your security settings. Initiate Rollback Local Update downgrade oneplus 9 to android 11 exclusive
If these issues plague you, is your only escape.
If the local upgrade fails, or if you want to ensure a 100% clean slate, the MSM Tool is the industry standard. This is a low-level flashing tool used by OnePlus service centers.