How to repair black screen?

Hello guys,

I replaced my battery on Samsung s20. I replaced it with a new one, reconnected all things back to their place (I did with the same steps as in ifixit tutorial on battery replacement) and everything worked. But next day phone somehow turned black, couldn't be turned on.

The I searched for the solution and came to the boot/ restart of the phone (with the power on and volume down button) and it worked again, at least two times, because after the logo or battery percentage (it displayed 54%) showed up, the screen started to flicker or it showed random colours. After two or three tries, it stopped showing anything.

At the moment it only vibrates and does sound when I connect it to the charger.

Any ideas how to fix this? Thanks.