Are you sure this is an issue specific to nwjs?
A blacked out canvas makes me believe there might simply be layers that aren't invisible and block the 3D canvas.
Please confirm this doesn't happen when simply previewing in your browser directly.
I ran it on my laptop, where I had previously lowered and allocated 1 GB for VRAM via BIOS, since I didn't have enough RAM for all the tasks. Then this happened. I tried it on another device with more memory, and it works there. Here, I also tried it in Chrome and got this error:
Uncaught TypeError: Cannot read properties of undefined (reading 'ClassName') at babylonjs.loaders.min.js:1:174181 at babylonjs.loaders.min.js:1:212420 at babylonjs.loaders.min.js:1:275 at babylonjs.loaders.min.js:1:288