ADB phone access via Windows 10

Unfortunately I broke the screen of my beloved 6P today and have spent the last 8 hours trying to figure out how to recover everything from it. It's still working as I can hear notifications and phone calls but the screen is blank.

After searching everywhere (xda, stackoverflow etc.), I'm a bit stuck and was wondering if anyone can help. Here's my plan:

1) I want to emulate the phone screen on my PC via USB using Android Control
2) I need USB debugging mode to access the phone via ADB
3) I need the correct (Google) USB drivers installed on my PC to access ADB

I have downloaded several tools/drivers and this is how far I got:

1) Windows sees/recognizes the phone under Devices and in Device Manager (as It does normally) - I am unable to access the phone because it's not in file transfer mode
2) When I run adb devices, the list is empty
3) I tried to update the driver to the latest Google USB driver but Windows 10 won't let me (windows has determined the best drivers etc. etc.)

I can't be sure what is blocking access via ADB. I'm sure I enabled USB debugging when I first got the phone but it was a long time ago. I read that I might need to disable Windows Driver Signing to install the latest Google driver but I haven't tried it yet.

My question is, how can I tell if it's USB debugging or the Driver? Any help would be greatly appreciated!