Downgrade Android 10 to Android Oreo

Please tell us some basic information before asking for help:
- Model Name:
- Firmware Version:
- Rooted or not:
- Frequency of Occurrence:
- APP Name & APP Version (If your issue relates to the app):
In addition to information above, please also provide as much details as you can, e.g., using scenario, what troubleshooting you've already done, screenshot, etc.
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Comments
Which built no is best?
How you downgrade to Oreo ??
Best builds of Oreo is 338 or 334..
Never go to 340 .. that's laggy n battery eater.
Flash the fastboot ROM of any Oreo build. It's easy if you have fastboot ROM, along with Adb & fastboot drivers installed in your PC/Laptop.
I don't have computer access now..can i downgrade without computer... Like flash from memory card in stock recovery mode ??
No.....................
But , recovery bootloader goes to black screen or dark.
How to fix this?
Device not certified in play product. How to fix it?
Which built no.
support native video calling?
Please tell me downgrade pie 087 to OREO build 338 with help of computer simple method please