3.0.2 (and below) mjml app custom engine doesn't work on Win10

[Skjolbir]

Describe the bug
I have used npm to install the 4.7.0-beta files, and no matter where I point the apps custom engine filepath to, it returns MJML not found at this location

To Reproduce
Steps to reproduce the behavior:
Create folder on desktop
use npm init to prepare that folder
use npm i mjml@next to install the mjml beta files
use the app (v3.0.2) and go to settings
use a custom mjml engine browse button to try to locate the correct filepath to use the beta engine
cannot find mjml at location

Expected behavior
the app uses the beta mjml instead of the embedded MJML engine.

Screenshots

Environment (please complete the following information):
Windows 10
app version 3.0.2

Additional context
Doesnt seem to work even if I use the stable 4.6.3 files.
Might be worth noting, the mjml file is just "file" filetype. I'm not sure if this is useful.
I downloaded v2.10.0 of the mjml app, and tried to direct the filepath to the stable 4.6.2 version on MJML downloaded through npm (npm install mjml) and that doesnt even work. Not sure this feature works at all on Win10 as far as I can tell.