First you must register for access
Register for Unreal Engine on GitHub
/README.md at Luoshuangs-GPULightmass-5.3-preview
Then check readme if you decide you want to build this, but you must have a NVRAM/SSD 512 GB hard disk or it wont build.
Git hub will not allow the BINARIES. Being an indie developer I am limited to 2GB max size repository.
Each repository is a link to another and they are source NOT BINARY.