Screen very dim Apple Logo out but works with External Display

Hi, community:

I’ve been using this retina MBP for about 7 years now. (Bought it when it came out Feb 2013). One day I cleaned the screen with moistened paper towel. Afterwards, screen went black and logo no longer lit up. When I shut all the lights in the room and use flashlight to aim through the Apple logo, I was able to see my desktop. But screen is very faint and extremely dim. I’ve rebooted multiple times. Nothing will make the screen brighter.

I am always able to use an external monitor with my MBP. There is no problem there.

I don’t know if this is related to liquid damage? Paper towel is not soaking wet. The computer is 7 years old but still going strong. I would like to have some hack around to make the screen work.