Can I revert to an earlier Android software version

[Android Central Question]

I am sick of this in-call screen timeout issue and believe that it came with the "Oreo" update. Can I revert back to the previous version until a fix is released?

 

[Rukbat]

I can't figure out exactly what you mean by "this in-call screen timeout issue", but sure, assuming 2 things:

1) There was a Nougat version written for your phone (and you can find a file for it)
and
2) Your phone's manufacturer doesn't "stop-loss" versions, meaning that once you update to 8, you can no longer install 7, 6 or anything earlier.

Just find a file for the Nougat version of android for your variant of your phone (model, country and carrier). Back up everything - flashing firmware fives you a brand-new phone. All your additions - apps, pictures, music, rooting, anything you did since the box was first opened - are gone. If you want to keep it, you'll have to back it up. (This includes apps - if you didn't update an app, and find that you don't like the updated version, that's too bad - unless you backed up the version you're currently running. See Backing up an Android Device.)

Then do whatever your phone needs to flash firmware - run Odin, unlock the bootloader, whatever - and flash it. Once that's done, and it sets itself up (which can take 15 minutes after the firmware is installed) set the phone up - Google account, name, email account, etc. Then restore the backed-up things to the phone. (You normally won't be backing up the email app, so you won't change what you've set up. If you're not running the stock email app, don't set your email up until you've restored the app.)

The whole process, from flashing the firmware to having finished getting the phone back to where it was, should take an hour or two, depending on how much you have to restore and set up.

Updating is just changing a few things in the firmware - "downdating", getting rid of an update, is restoring the entire phone. The older version is no longer there after an update, so there's no quick way of "removing the update", and there's no "downdate" file.

And the issue you're talking about is probably something that can be set to the way you want it to work without reflashing an older version. I've never had either my phone or my screen time out during a call, and I'm running 8.1. (The screen does go black while the phone is against my ear - that's to prevent "cheek dialing" - but it comes back on as soon as I remove the screen from my ear.)