Thankyou!
It's random, but after playing a game someone else made, weeks later I realised that all my own RPGMaker game projects could no longer be test played properly, and could not understand why.
It turns out, the other game I played, it had messed up NW.js in my file system somehow. I searched around a long while not understanding, but this article gave me the needed information to discover the issue! Plus also now a better understanding of various other things. :D