Hey there teodora65,
Thanks for reaching out to Apple Support Communities. It sounds like there could have been some physical damage to the display when your iPhone was dropped. I’ll be happy to help with this.
Just to be sure this isn’t something related to software, restart your iPhone and see if this has any impact on the issue:
Restart your iPhone
If that doesn’t help, try adjusting the brightness or adjusting the True Tone or Night Shift settings and see if this has any impact on this:
Adjust the brightness on your iPhone, iPad, or iPod touch
If this doesn’t help, this most likely is related to your iPhone hardware and you’ll want to reach out to Apple Support at the following link to look further into this with you:
Get Support
Take care.