Maybe you regret making the leap to oos11 on your OnePlus 7 Pro and want to go back to clean, old, smooth, oxygen OS 10...

...if so, here's a fail-safe guide to ensure you get it done:

1) BACKUP!

Rolling back to oos10 will FULLY WIPE your device! This is inevitable.

I recommend connecting your phone to your pc, copy any pictures and videos you'd like to keep and haven't uploaded to a cloud storage system like google photos (e.g. : screenshots and downloaded pictures ) (there are pictures stored in the "pictures folder" but also the "DCIM" folder). Copy any app data you'd like to keep by copying the folders those apps have created in internal storage. Think of ringtones, music, chat history and documents you want to keep. After you have copied those files to your computer, I recommend doing a backup of your apps, contacts, notes, system settings, calls ans SMS's via the OnePlus switch app. that backup will be stored in the "opbackup" folder in your internal storage, copy that folder to your computer too.

After having done all that, you should be able to use your phone as usual after having gone back to oos10.

2) The Fast way (MAY FAIL and become the slow way)

OnePlus offers a special file for rollback from oos 11 beta to oos 10 stable in this thread

After having downloaded the file which I have uploaded a copy of to gdrive here (OnePlus Official Rollback file), you copy that file to your internal storage (meaning outside any folders) and make sure the file ends in .zip, otherwise remove the .jar characters with the backspace button. Then, go to settings>system>system updates>settings icon (top right corner)>Local Upgrade. There your file will appear. Click on it and select install now.

This didn't work for me, I always got "update failed" immediately after it starting.

With other files I got "the version of your selected package is lower than that of the current system".

So if that happened, here is the workaround I found:

3) The Safe Way (should also be fail-safe)

This method consists of Rolling back to the original software the OnePlus 7 pro was released with (oos9) through a special OnePlus file. Then update the phone through the same method to the oos version of your choice.

Here are the step by step instructions:

1. Download The Fulldowngrade to oos9 file for OnePlus 7 Pro or for OnePlus 7 depending on your model. I uploaded a copy to gdrive in case the link doesn't work. (see below for Oneplus 7T/7TPro files)
2. Copy that file to your internal storage (meaning outside any folders) and make sure the file ends in .zip, otherwise remove the .jar characters with the backspace button.
3. Go to settings>system>system updates>settings icon (top right corner)>Local Upgrade
4. Click on the fulldowngrade file and select install now

After the process is complete, you should be on android 9.

To update to oos10, you should find the oos10 update file on the OnePlus website (update: latest oos10 builds can be found here) . (I included the oos 10.0.11 update file for the 7 pro on the gdrive too)

Repeat step 2 to 4 with the new file.

And Voilà! You should be back on Oxygen OS 10 now.

4) Getting your files back together

When you have your phone back up and running. Copy the files you want back on your phone from your PC to your OnePlus alongside the opbackup file, overwriting the one that is currently on your phone. Through the OnePlus Switch app, use the Restore Backup option to get your contacts, setting, etc... back. To install Apps go to the opbackup file where you will find them. Some are split, to install split .apk's I recommend installing SAI from the Google Playstore.

There you go. Hope this was helpful and that this will make your experience better again.

Comment or message me for any further questions :)

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Edit:

Here is u/TXdevs 's comment with the files they found for the 7T AND 7T Pro that should downgrade your phone to the OS it shipped with.

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" Below are the links to the MSM Download Tools for the 7T and 7T Pro.

These can be used to downgrade, as well as revive bricked devices.

Follow the instructions in the threads - YOU WILL LOSE ALL DATA, so backup all your files.

OnePlus 7T MSM Tool

OnePlus 7T Pro MSM Tool

Mirrors are also hosted on OnePlus Community Server under "Unbrick Tools" "

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Kudos to TXdevs.