I made the mistake of building “as is” after the Generate created the project and got this same error. When I looked up how to build, I realized I had forgotten to set the UE5 project as the starter project. After I did that, and a billion years later, it compiled and ran. It has been awhile since I built source, so maybe it was just newb mistake, but thought I would share.
I followed this: Building Unreal Engine from Source | Unreal Engine 5.0 Documentation