Macbook pro boots to a black screen after a few seconds of use A clip of what exactly is happening: https://drive.google.com/open?id=19FSU3wFnCi9QjXQRO4UrTT-KxuooOYLu

I've tried all the tips here: https://ugetfix.com/ask/how-to-fix-mac-booting-to-black-screen-error/
including SMC reset, PRAM reset, etc.

An important note is that the computer itself is on - i.e. I can type the password and go on terminal, play music successfully, etc. but the display stays off (not completely off, it's slightly lighter than when the computer is completely off).

Edit:
Huh. After a few days, the problem completely disappeared randomly. I ran the Apple Hardware Test and no problems showed now. Very weird, but at least I'm glad the problem is resolved. Thank you for your help.
The video is not very clear to understanding the issue. It seemed like you clicked on the “Ansel Admin” username and it blanked out. Then you clicked the power button and it came back to login screen. Also, it will help if you describe what you are doing and the problem (in the video as a voiceover :).

Here’s what you can try.


If you have a monitor available, check if you can see the display after logging in.


There are two ways I found to increase screen brightness (as you mentioned that it was not fully blacked out). (Links to original articles below). 

Method 1: Using osascript, key code 144 (brighter), 145 (dimmer)

$ osascript -e 'tell application "System Events"' -e 'key code 144' -e ' end tell'


$ osascript -e 'tell application "System Events"' -e 'key code 145' -e ' end tell'


Method 2: Using Homebrew - https://brew.sh

If you have homebrew installed, you can install brightness to control.

$ brew install brightness


$ brightness 1


$ brightness 0.5


I have tested the osascript commands on Catalina 10.15.4. You will need to give the terminal accessibility permissions.

If these don’t work, try booting in Safe Mode. 
If it resolves the issue, it may be some startup item that could be causing this.
Hold down the Shift key when powering up and you hear the startup chime to enter Safe Mode.

Links:

How can I dim the screen from Terminal?

How to Adjust Screen Brightness from Terminal in macOS
https://www.maketecheasier.com/adjust-screen-brightness-from-terminal-macos/