I downloaded the latest stable executable (LAMMPS Binaries Repository: .) of lammps as it was explained in this video (https://www.youtube.com/watch?v=GXA2PyqKYdY&list=PLEwB0P-kIa7JF9Vy2O-Az5mmeJFmnRExZ) but the command lmp_serial.exe can’t be found.
It looks like the executable is not on your path.
Besides, you better follow the official documentation. Or plague the youtouber, instead.
This must be a very old video. The LAMMPS executable in the pre-compiled packages for Windows has been called just lmp.exe for many years and that is documented behavior: LAMMPS Windows Installer Repository