Downgrade your android device to android 10

Caution: This is only to unlock the oem of your mobile
phone and should be done only if you have android
12 or above in your device

Enable Developer Options:

1. Head to settings on your device.

2. Click on about device
   

3.Tap on Build number 7 times to enable developer options

1. You will get a popup saying that you are a developer now.
   

2. Head to developer options on your phone and turn the
   on advanced reboot and USB debugging.
   

3. Connect your phone to your PC with a USB cable.

7.Once you've backed up all of your data, you'll need to
download an Android factory image of the version you want
to go back to. You can find this at the manufacturers
website if not then best place to find it is XDA forums

1. Download the SDK platform tools if you are using windows then,

   1. Extract the zip file to the desired location.

1. Navigate to the platform tools folder and type cmd in the search text-box

1. Then type

adb devices

in the command prompt. You will get a string with the device being connected to your pc

1. Type

adb reboot bootloader

in the command prompt.

1. Your device will reboot into fastboot mode.
   

2. Now you learnt how to set your phone to fastboot mode.

3. Press the power button and boot your device.

4. Search for your local updater apk (for oneplus it is
   oplocal updater

5. Caution: remember to do this in fastboot mode
   From the stock rom you downloaded, take the .img file
   and type the following command in the same directory
   

fastboot flash bootloader [bootloader file name].img

1. Downgrade to the desired version by selecting it in the apk installer.

Now you are good to go your mobile phone will be downgraded to the one you like.