So I've got my phone back, it's a OnePlus 3 running Android 8.0. And I found that your steps are incorrect 
Here is a correct guide:
Important note: This guide assumes that you haven't removed your SIM card since your phone got broken. It also assumes you have only one SIM card installed. It could be the case that extra or different screens appear when the SIM card is removed or added again! I could test later if the steps need to change in the case the SIM card was removed from or re-added to the phone.
This is a blind guide, so you might actually break something by performing these steps. This is at your own risk by attempting to try out this guide, so only consider this as a last resort.
Make sure you have an OTG cable to connect an USB keyboard to your phone. Start with your phone turned off. To do this, hold the power button for about 8 to 9 seconds. If you hold it longer than you will feel a vibration and the phone reboots. To check if your phone is turned off, slide the button on the left side of the phone up and down. If you don't feel any vibrations it's turned off. If you had your keyboard connected and it has a back-light then the back-light will turn off when your phone is turned off.
It's recommended to keep the side button slided all the way down in 'Ring' mode so you get as much feedback as possible. The phone does NOT vibrate when you put it in 'Ring' mode. It only vibrates when you put it in 'Silent' or 'Do not Disturb' modes.
Connect your USB keyboard to the phone if you haven't already and turn on the phone by holding the power button for about 2 seconds until you feel a vibration. Wait for the initial boot sequence. You can press Escape during this time. If you don't see the lights of the 'Back' button and 'Recent Apps' button on your phone light up, the initial boot sequence hasn't completed yet.
Getting into Android:
- Press escape a few times and verify that the 'Back' button and 'Recent Apps' button lights on your phone light up. This also activates the screen.
- Enter your PIN using numerical buttons on the keyboard (don't use NumPad)
- Press Enter
Android is now booting. This will take some time. During this time the keyboard is not responding. Press Escape a few times and check if the 'Back' button and 'Recent Apps' button on your phone light up. If they don't, then Android is still booting. If they do then Android has booted. After a fresh boot of Android you must unlock your phone by entering your PIN.
Unlock the phone:
- Press escape a few times and verify that the 'Back' button and 'Recent Apps' button lights on your phone light up. This also activates the screen.
- Enter your PIN using numerical buttons on the keyboard (don't use NumPad)
- Press Enter
You've now completed the mandatory PIN after a fresh boot of Android. However you're not immediately redirected to the Home screen. The phone is still locked. Perform the next steps to unlock the home screen.
Getting into the home screen:
- Press the Windows key AT LEAST two times to activate the screen and to bring up the 'Enter PIN' screen. Pressing the Windows key more has no extra effect, so you can press it a few times to make sure the 'Enter PIN' screen shows up
- Enter your PIN using numerical buttons on the keyboard (don't use NumPad)
- Press Enter
- Press Escape a number of times to make sure that any notifications or startup apps are dismissed and you are in the home screen.
Getting into the settings menu:
- Press Windows + N to bring up the pull-down menu
- WAIT ONE SECOND! If you do the next step too fast, the settings button won't be selected.
- Press TAB to bring focus to the Settings button
- Press Enter
Enable Developer Mode:
- Hold the 'Down Arrow' key for at least three seconds. This navigates to the bottom of the settings menu to 'About phone'
- Press Enter
- Hold the 'Down Arrow' key for at least two seconds. This navigates to the bottom of the 'Phone Status' menu to 'Build number'
- Press Enter 7 times. (Pressing it more times doesn't have an extra effect)
- Enter your PIN using numerical buttons on the keyboard (don't use NumPad)
- Press Enter
You are now a developer! Nothing happens if you were already a developer and you try to perform the last two steps.
Now, get back to the home menu by pressing Escape a couple of times.
Then perform 'Getting into the settings menu' again. If you want to make sure you start clean, then perhaps lock the phone with the physical button on the right side of the phone and perform 'Getting into the home screen' and 'Getting into the settings menu' again. When you're in the settings menu, perform the following steps to enable USB debugging:
Getting into Developer options:
- Hold the 'Down Arrow' key for at least three seconds. This navigates to the bottom of the settings menu to 'About phone'
- Press the 'Up Arrow' key 2 times. This will navigate passed 'System updates' to 'Developer options'.
- Press Enter
Now we are in the Developer options menu, but enabling USB debugging is tricky. On my phone with Android version 8.0 it takes 15 'Down Key' presses to reach the USB Debugging option. You have to start from the top of the menu (which is where you are when you open it), because starting from the bottom is even more error prone since you need to navigate passed about 50 options.
Enabling USB debugging:
- Press the 'Down Arrow' key 15 times. This navigates to the USB debugging option
- Press Enter (This brings up a popup to enable USB debugging)
- Press the 'Right Arrow' key or TAB to switch focus to the OK button
- Press Enter
USB debugging should now be enabled...
Last edited: Jan 21, 2018