[General Questions and Answers] _sepiroth:
Thanks a bunch, that pointed me in the right direction with my research! I solved my issue, I can now control my phone from my PC.

By doing this I ran into a couple of problems, I'm going to describe them and their solutions:

Problem 1: couldn't ADB into the device when in Recovery Mode. That is because after a long head scratching session I came to the conclusion that I didn't have TWRP Recovery installed (I had Philz Touch CWM Recovery and LineageOS 14.1 instead).

Solution 1: ADB mode is enabled in TWRP by default. So I flashed the latest TWRP through Odin, ADB instantly started working afterwards in Recovery Mode.

Problem 2: USB Debugging was disabled inside the OS.

Solution 2: from the thread that Ibuprophen posted, you can enable USB debugging in your OS by opening an ADB shell into your device and modify the build.prop like so

Adb shell
echo "persist.service.adb.enable=1" >>/system/build.prop
echo "persist.service.debuggable=1" >>/system/build.prop
echo "persist.sys.usb.config=mass_storage,adb" >>/system/build.prop
reboot﻿

Problem 3: /system was empty so there was no build.prop. If I attempted to create a build.prop file it wouldn't be saved after a device reboot, so USB debugging still didn't work.

Solution 3: it seems like TWRP doesn't mount /system by default, only /data. You can mount it manually through ADB like this:

mount -o rw /dev/block/bootdevice/by-name/system /system

I found this out from this stackexchange question: https://android.stackexchange.com/q...data-partitions-in-recovery-mode-in-adb-shell

Problem 4: When an app tries to use USB Debugging you need to allow it to do so from the phone. Since the screen was broken, I couldn't do this.

Solution 4: You'll need to push a public key to your device with ADB. Boot into Recovery Mode and make sure your device is recognized by your PC and type

adb push <path to adbkey.pub on your PC> /data/misc/adb/adb_keys

This solution is from: https://stackoverflow.com/questions...b-rsa-key-with-broken-touch-screen-on-android

This will make sure that you won't need to confirm debugging permissions for apps coming from your machine.

So for anyone who has a broken phone screen (my screen is dead and touchscreen/touch buttons are kaput too) and wishes to control their phone from their PC but USB debugging is disabled:

1. Boot device in TWRP Recovery (flash it if you don't have it)

2. ADB into the device

3. Make sure /system is mounted (if it's empty it means it's not mounted), else mount it manually like in Solution 3

4. Configure build.prop to have USB Debugging enabled like in Solution 2

5. Push your public key to the device like in Solution 4

6. Restart the phone (into its OS)

7. Download the Chrome extension called Vysor and launch it

8. Connect your phone through a USB cable

9. The device should appear in Vysor, connect to it and have fun controlling it

Note that if you just want to backup your files, steps 1 + 2 are sufficient. After making sure ADB works you can just 'adb pull' all your files which should be located in /sdcard. Google it, it's easy to find.

The same goes for backups, you can do them directly through ADB.

Again, thanks Ibuprophen!