S20+ Screen black but touch works

@willl84 based on this "It did get dropped in water about 24 hours before" and this "but other than the "moisture in charging port" message it was perfectly fine" It probably was ok, until it shortened out the screen.

For now you need to stop continuing to try to charge, sync or otherwise use your phone. This potentially can make a bad situation worse. This may further damage your phone.

The next thing to do is to clean it. Use the guides from here Samsung Galaxy S20+ to work on your phone. Remove the main board and the charging board. You will have to remove all the EMI shields off those boards. If you do not remove the shields, you are not cleaning the board.

Take a close look at all components and connectors to assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. . Once you got any gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for an Apple iPhone 3G but all the steps are still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. While you clean your boards, check for any obvious damage, like burned or missing components etc. The importance here is the cleaning.

When it is properly cleaned, replace the battery. This is a must and not an option. It will fail if you do not take care of it now. All these steps are to avoid delayed failure caused by corrosion. Best thing to do would be to clean it with an ultrasonic cleaner, but if you do not have access to one, this will at least help. Once all this is done, reassemble your phone and reevaluate. Until it is cleaned, everything will only be a guess. It is possible that you have a bad display assembly or shortened out video circuit on your main board. Most likely suspect for me is the display. Replacing the display assembly may fix it.