this tutorial counts for NWJS 48.4 or higher (might be for some lower version).
MV start with 0.29 and the game resolution start in the center.
when you update the NWJS it always start in the upper top-left corner and cannot be set
to the center or coded to make it effective.
this require YOU as dev to code a single line of code to the package.json file (as shown below).
toolbar might crash if used while coding for higher version as this is REMOVED, probably called
differently but has no effect on the game itself (this require some coding to disable it effectively).
the width/height are probably changeable by plugins useage and altered there dynamicly.
but once you set position to center as shown, this start your game in the center of your screen,
not in the top-left corner.
so if you use a different version of NWJS other then 0.29 or does not work in MZ, this might work
for you as well