Stickied Post
As always:
Hi guys,
since many people liked the written detailed rollback guide when we had the Android 10/Q Preview last year, let's just throw this one in for 2020 as well! 
Sir, how do I go back to Android 10?
Prerequisites
Video guide
I prepared a video guide for this, as many people loved the written one. However, it did not look good with the screenshots. So, here is the guide:
Written guide
A: Take a backup of your stuff. Everything will be erased once you flash the rollback build, so do a backup of your nudes before doing anything.
B: Download the rollback build that fits your device.
If you are opening this from the Community app, you will get a white screen when you tap a link. On that white screen, tap the three dot menu and choose "Open in browser".
This will start to automatically download your file.
- Download links for OnePlus 8:
- Download links for OnePlus 8 Pro:
C: Rename the file. (The reason for this is that the rollback build, for some reason, is downloaded as a JAR file, while the updater needs it to be a simple ZIP file.)
Go to the File Manager app and navigate to the downloaded rollback build.
For example, if you are a European user with an 8 Pro, you should rename OnePlus8ProOxygen_15.E.17_OTA_017_all_2005100255_downgrade_2d24414aaa814738.zip.jar to → OnePlus8ProOxygen_15.E.17_OTA_017_all_2005100255_downgrade_2d24414aaa814738.zip
(Just get rid of the .jar extension)
D: Move the file.
The official guide says "root" directory. What is this? Well, doesn't have anything to do with rooting your device.
It's just the thing that you see when you open the File Manager first.
E: Flash the rollback build.
Follow these steps to get there. Your last chance to backup all your stuff, just saying! 
- Settings
- System
- System updates
- Gear icon (upper right corner)
- Local upgrade
- Tap the file
Thanks for reading, hope I could help a person or two.
Last edited: Aug 17, 2020