I have just fallen foul to this…
Unhandled exception: System.IO.FileNotFoundException: Could not find file ‘C:\Program Files\Epic Games\UE_5.0\Engine\Binaries\Win64\UnrealHeaderTool.target’.
The project was working fine just prior to my rebuild and now the file is missing?
Solution: I went into the Launch > Options via the Launcher and forced a rebuild by disabling one of the platform options.