@aayush447 Serveronly is included with the MagicMirror framework. What it does is skip displaying the interface on the Raspberry Pi via Electron and the HDMI video output. You can still see the interface by pointing a web browser (especially the browser included with the Raspberry Pi operating system) at the Pi. But the Pi itself will still display the desktop and/or command prompt.
This is especially useful for people who remote in to their Pi for development, multiple displays or remote access. For example, you could have one Pi run the MagicMirror framework and have a mirror in your bathroom, a display in your kitchen and a display in your man cave all showing the same output of the Pi.
I use node serveronly during my development on my office PC. It lets me use a web browser to view the interface, which I can resize, move to a different monitor, etc. Otherwise, Electron would take over one entire monitor to display the output of the Magic Mirror framework.