A warning will appear stating this will reset the device. Tap Install Now
You will see a progress bar. The screen may flicker – this is normal. Downgrade Oneplus 9 To Android 11
If running OxygenOS 12/13:
Android 12/13 hides the "Local Upgrade" option. You need to install a helper app: A warning will appear stating this will reset the device
To downgrade your OnePlus 9 Go to product viewer dialog for this item. Downgrade Oneplus 9 To Android 11