If you're a OnePlus 7 or 7 Pro user running Android 10 and you've sifted through the different navigation options available for your device, you probably noticed that two-button navigation is no longer there. For proponents of this UI, such news might be pretty disheartening.
Well, grieve no more, two-button devotees! There's a way to resurrect the sweet harmony of modern gesture navigation and the coveted "back" button of yore, and it just takes a bit of ADB intervention to make it happen.
To begin, you'll need to download the latest version of Android Debug Bridge to your computer; for the most straightforward method, check out this Nexus Tools installer for Mac and Linux, compiled by Android Police's Corbin Davenport; Windows users can download the required SDK Platform Tools from here separately. You'll also need to enable USB debugging on your device, which you can do by following this path: Settings -> System -> About Phone -> tap build number 7 times to enable Developer options, then enable USB debugging via Settings -> System -> Advanced -> Developer options).
Next, make sure your phone is connected to your computer. Set the current navigation setting on your phone to the standard 3-button layout. Then open ADB and execute the following command:
adb shell cmd overlay enable com.android.internal.systemui.navbar.twobutton
And that's it! You should now see two-button navigation in your settings app.
Two-button navigation isn't expected to return in the final version of Android 10 for the OnePlus 7 and 7 Pro, so you may want to bookmark this page in case you need this information again as the updates progress.