Yes, fix sgcmc has been cleaned up and integrated into the LAMMPS distribution as part of the MC package, so there is no more need for the plugin package.
Just ignore those. They are part of the automated build scripts that I use to build the packages. The admin packages change to admin mode to install LAMMPS for all users (was required for very old Windows versions). The msix packages are for creating LAMMPS packages for the Microsoft Store. Both are in the process of becoming obsolete, see Planned Changes to LAMMPS Windows Installer Packages