Hi,
Given that the screen had two small cracks already, the drop may have contributed to the internal connections in the screen being damaged further to the point of causing the problem you have now.
You can’t see internal damage in the screen, you can only notice the effects it has.
It could also of course be a display flex cable connection problem i.e. loose or worst case it is a systemboard problem.
As a DIY repair all you can initially do is to open the phone and check if the display cable is securely attached to the systemboard and if it is, is to temporarily replace the display and check if the problem is still there or not.
Here’s the ifixit [guide|136889] guide that will help.
If doing this yourself is too daunting, contact a reputable, professional mobile phone repair service and ask for a quote