Files like these are and not official releases from Epic Games. It is standard practice to: Scan the .rar file for malware using tools like VirusTotal .
Ensure you are downloading from a verified source within a known modding Discord community. Fortnite 3.5 reupload by blk.rar
The specific version of Unreal Engine 4 files required to run that build. Files like these are and not official releases