Select the you placed in the root directory earlier.
Install the APK. You may need to grant permission to "Install apps from unknown sources." Downgrade Oneplus 9 To Android 11
Install and open the you downloaded earlier. Tap the gear icon in the top-right corner. Select the Android 11 rollback package from your storage. Select the you placed in the root directory earlier
You are trying to downgrade from Android 13 or OxygenOS 13.1 directly to Android 11. Fix: You must first downgrade to Android 12 (OxygenOS 12) using an intermediate rollback package, then downgrade to Android 11. OnePlus blocks direct major version downgrades. Downgrade Oneplus 9 To Android 11