I was actually just testing this last night as i own a repair business.
iphone 7 and iphone 8 both original screens .
my way of testing iphone 7 screens (mine all use the original apple lcd and touchscreen) is to attach the screen only , no front camera or home button. It will appear to boot loop but it takes 4 mins 10 seconds to get eventually to home screen . During some of this time i use it to check for any visual defects on LCD.
now my findings were the iphone 8 screen booted up in the same time 4 mins 10 seconds on the iphone 7. LCD fine but touchscreen not working at all.
HOWEVER........ it has only came to light that ios 11.3 is preventing iphone 8 users that have had a COPY screen on their iphone 8 now have no touch. Copy screens worked fine on previous ios.
i am wondering if the iphone 8 touchscreen would work on my iphone 7 if the 7 did not currently have ios 11.3 installed . I would bet my bottom dollar the touchscreen would operate as normal.