Do you use plugins? Do you use C++?
MSVCRT.lib(exe_winmain.obj) : error LNK2019: unresolved external symbol WinMain referenced in function "int __cdecl __scrt_common_main_seh(void)" (?__scrt_common_main_seh@@YAHXZ)
UATHelper: Packaging (Windows (64-bit)): UnrealBuildTool: C:\Users\\Documents\Unreal Projects\Launch\Binaries\Win64\Launch.exe : fatal error LNK1120: 1 unresolved externals
It Looks like something isn’t linked very well. That could be a plugin or something with you C++ files.