ORRH is officially supported on Windows 10 only. You may encounter issues when on older or newer versions of Windows.
for linux

1. Go to the .NET Download Page, and download the x64 SDK Installer. This will download a few dependancies that are not required aswell, though. If you do not want them, download the x64 installers on the right side. The SDK install is recommended as it is quicker.
   
2. Download the most recent verison of ORRH from the Discord or the itch.io page.
   
3. Install VC Runtime 2005 and 2008. This will fix “side by side configuration” errors.
   
4. Extract the 7z file with a file archival tool like 7-zip or WinRAR. In the case there is a patch available, extract it over the files of the full release, and replace any files.
   
5. Run OnlyRetroRobloxHere.exe
   
   

There is also a video guide, but it may become outdated, and is not very professional.