Chosen Solution
So i dropped my iPhone 8 and when it fell the display didn‘t function anymore altough the glass was intact. At first when I used the power button the screen did turn on and off (just like a tv without any channel on; you could see that it has elecricity but it was a black screen tho). After i made a hard shut down (pressing the keys) the screen was just plain black (no electricity) but everything functioned (except you know… the screen). I thought maybe the LCD or touch might be broken and bought a replacement screen. Long story short end, nothing changed after replacing the screen
It sounds like you have damaged the backlight circuit on the logic board. You can check this by shinning a torch on the screen and see if you have an image. The backlight circuit will have to be repaired by a competent technician as microsoldering will be required.
