npm run watch gives "TypeError: mix.copyDirectoryWatched is not a function"

Problem/Motivation

Running npm run watch terminates in error "TypeError: mix.copyDirectoryWatched is not a function".

Steps to reproduce

Install radix and subtheme as per directions on project page. On Windows 10, I installed npm as per:
https://support.symphony.com/hc/en-us/articles/360045337451-Symphony-Dev...
Created and enabled subtheme as per instructions. Using MINGW64 git bash shell installed as per Git for Windows, I get the above error.

Proposed resolution

In webpack.mix.js add the following after mix is defined:

require('laravel-mix-copy-watched');

as per the usage instructions for the node module laraval-mix-copy-watch readme instructions:
https://www.npmjs.com/package/laravel-mix-copy-watched

I am not familiar with the radix build process so there may be another solution or some reason why I needed this and others don't. I can offer a patch if it would be useful. I left the priority as normal since I assume others are able to build without this change. If that assumption is wrong, this should be critical since it prevents use of the theme.