Solution: Go to Settings → Video → Change the "Video Device" to "ManyCam Virtual Webcam". Then restart the software.
Once you have downloaded the installer (usually named something like ManyCamSetup-4.1.2.3.exe), do not run it yet. Download Manycam Old Version 4.1.2.3
Old installers are a common vector for trojans because users disable antivirus to run "cracks" or legacy software. Solution: Go to Settings → Video → Change
Many classic plugins (virtual green screen tools, old PTZ camera drivers, Flash-based overlays) never received updates for ManyCam 6+. 4.1.2.3 retains backward compatibility with DirectShow filters from 2010-2015. old PTZ camera drivers
Before clicking any download link, understand why this specific version has achieved cult status.