The screen is black, but the phone works (even the touchscreen).

My P20 Pro turns on, sounds, receives calls, and even the touchscreen works (I can get to the dial and it makes sound when I touch); but the screen is pitch black.

What I tried:

• Restarting it to see if it’s a software issue. It restarts, but the screen is still black. I even tried to go to recovery or bootloader and the screen still is black.
• Opened it up to see the screen connector. It wasn’t loose, nor dirty or corroded. I cleaned it up regardless, but still it doesn’t work.

So, I want to know if someone has experienced something like this… I don’t know if it could be a screen problem (since it’s in mint condition and the touch works), or it could be something related to the motherboard.

Any ideas? Thank you in advance!

Edit 07/10/2020:

I checked out the screen for a backlight issue, and I didn’t saw any images, but I noticed this blueish line underneath the phone, followed by a faint dark thick line. It covers the whole bottom of the screen. Could that be signs of damage of some sort?

It also goes up a bit from the side.

Edit 23/10/2020:

A CHANGE OF SCREEN FIXED THE ISSUE.

Before the change I fully opened it up, and it showed that water entered from the bottom right speaker. The mic board was fully corroded, and that blueish line that I saw inside the screen was indeed corrosion.

Thank you for guiding me in the right direction!