Why is the phone in a boot loop after screen replacement?

Hi all - I've changed the screen on a friends iPhone x and it is now stuck in a boot loop. I have changed iPhone X screens probably. 20 + times and never had this issue and I don't think that I damaged anything this time round either.

Initially it would only boot loop whilst on charge and would do nothing at all when not plugged in so I thought perhaps it had to do with power delivery so I changed the battery too. Now it still boot loops, but both whilst plugged in and not plugged in.

I've tried hard resetting it on the phone itself and it didn't do anything. My PC. also won't recognise it when I plug it in via USB so I can't do anything in iTunes. Any ideas? Please help!