As of March 2021, Viewer is only supported on versions of Microsoft Windows supported by Microsoft. Before March 2021, Viewer ran on Windows, Mac, and Linux. At that time, we dropped support for Mac and Linux due to low demand.
Steelray Project Viewer runs on most modern versions of Windows (32-bit and 64-bit). When Microsoft discontinues support for a version of Windows, we do the same with Viewer on that platform, since we're unable to receive fixes to the operating system from Microsoft.