Top half screen don’t work only bottom

First disconnect the battery. Not unhook the screen and check the pins on the connectors on the screen and motherboard for any bent pins. Clean the connectors with a qtip and alcohol and a soft brush. It's possible that it's a bad connection. Also verify that that the image is there buy really hard to see because of back light. Is there is a possibility that you damaged the backlight circuit when you changed the logic board.

It sounds like you blew the backlight circuit and possibly the touch on that half of the screen. Did you disconnect the battery before you changed the screen? It's a common problem that people don't disconnect the battery and it shorts out the backlight circuit. You will need to take it to a repair shop who can microsolder.

Came across the same issue tonight, I had two XS units and 3 OEM screens. I found that for some reason, when I swapped the screens over one worked fine on one XS (XS_A)while the other one the top 3 row of icons was dead(XS_B). Yet I could swap another screen on XS_B and the screen would work fine. This proves that the logic board was fine & when I put the supposed half dead screen back on XS_A (original paired phone) the screen worked fine. The only difference I could see was…XS_A was on iOS 13.6 and XS_B was on iOS 14.1. Makes me wonder does iOS 14 have software checks that disables part of the screen if it’s not it’s originally paired screen…