Sleep? Is there a definition for that? :)
To note: the npm process starts up Electron in kiosk mode on the rpi. Electron is simply a browser, which then loads the localhost address to MM². So if you know your rpi’s address on your network, you can load it up anywhere through a browser.
In case you haven’t seen it, I posted how my (development) setup is, and it hints at doing just that with a remote browser:
https://forum.magicmirror.builders/topic/265/my-setup-or-how-crazy-i-am