How to figure out what is causing Fatal Error on packaged build?

So I’ve completed my first project in UE5 and come to package it. It’s run through everything and said it’s all complete. I go to run the .exe file to check and it’s all fine…on my machine.

I asked someone else to run the .exe on their machine (with identical specs) and when it boots it gives a Fatal Error message.

How can I find out what’s causing this?