Why is there a spreading black spot on my screen?

"I've said it before and I'll say it again...The rice myth kills too many phones!

You are fortunate that your device is not completely disabled but then again, by powering it on, you are accelerating the corrosion (oxydation) process internally. The spot on the display is caused by water. You will have to replace the screen assembly. You should back up your data while you can.

The water is inside the phone, on the logic board and under the shields, even under the IC's. The rice is nowhere near where the water is. So while it may soak up some water vapour, the real problem is the corrosion that is taking place as the water evaporates. The longer you let a phone sit in rice, the more time you are giving corrosion to damage your logic board. The saltier or harder the water is, the more damage will occur.

Here are some things you can do now:

Open your phone and remove the logic board Inspect the logic board, especially around the connectors and look for corrosion.Inspect both sides of the board. Unfortunately, 80% of the board is covered in shields. That's usually where the damage is occurring.Put your board in a container with >90% isopropyl alcohol and let it sit for a while.Use a soft brush, like a toothbrush and lightly brush away any corrosion you see.Rinse in alcohol and repeat.Let it air dry for a day.Re-assemble and hope for the best.

Your best bet is to find a professional repair shop that does water damage repair. They have access to pro-level ultrasonic baths and specialized cleaners as well as the skills to troubleshoot your board."

I'd pay the 37 dollars that is super cheap in comparison to 100-200 for a new Samsung S20 screen.. If you have determined its pixel related then some pixel fixes work depending on the severity… If its what appears to be ink leaked under the glass, somewhere you have cracked those layers in the screen releasing the liquid underneath the glass.. A screen when separated has many layers between the front and back of screen and is made of super thin mirror/ holographic like plastic material.. Mine just so happens to go away and then return if I apply to much pressure..

"I have the same problem too. A math teacher of mines knocked my phone down when we were taking a snap. The thing is the rice myth does not work. It damages the logic board. The only solution is to get your screen/LCD fixed or do it yourself which cost about 30 bucks but takes lots of time. One thing is, don't use rice. Here are some ways you can dry off your phone.

Blowing it off with a blowdryer for 15 minutes or more.

Let the phone and battery separate sit out for a day or 2 depending on the temperature.

Don't connect it too a charger. That will shut down electricity for an average 3 days or 2.

That's all I know about this subject. But it could be battery oil, dead pixels, corrupted screen damage. But if you see it your LCD is already damaged."