Answer for IPhone 6 Touch Not Working
In this case, the fault may be related to the logic board. For iPhone 6 and 6 Plus models. There is a design flaw for touchscreen ICs. which will cause the connection between the logic board and the IC not stable after being dropped. And a gray flickering bar will show up at the top of the screen.
If this is your case, you can resolder the touchscreen IC.
A video guide for your reference: https://www.youtube.com/watch?v=xr7tuFu4Y3Q&t=157s