How can I make a mac installer for electron app from a windows pc?
When I run npm make it making a windows installer only
If you want the app to be signed it has to be done on a MacOS, and also requires giving money each year to Apple: https://www.electronjs.org/docs/latest/tutorial/code-signing
If you are only distributing to Mac users who trust you, i.e. who are willing to ignore the security warning they get shown, then you can build for Mac on any of Mac, Windows and Linux. Electron-packager can do this.