generator-starter | Yeoman Website Starter Generator | Generator Utils library

Disclaimer: It's impossible for me to reproduce your error given that a) I'm on Mac, b) I don't have Photoshop and c) I didn't watch the video tutorial. Still, if you bare with me, I'm pretty sure the following will hint you in the proper direction.

The error you are getting is not actually related to socket.io or engine.io. Any dependency that you would declare from your plugin (and that it is not already a dependency of the generator) would trigger the same issue.

The problem is essentially that your plugin's node_modules directory is not actually used for dependency resolution. I'd expect that you can confirm this by adding something like console.log(require.paths) at the top of your plugin's source file.

Then why is it not used? Because generator hijack modules resolutions to disallow loading dependencies from outside of your plugin's node_modules (see Generator's main file: app.js). Note that this is a recent change (July 15, 2020) which explains why the setup you use may work in the tutorial but no longer works.

Now, I'm not sure exactly what's wrong with generator's patched module resolution. Apparently, it doesn't support symlinked plugins directories, but then again, I don't think this is your case. Could it be that some of your dependency may have been hoisted to a parent node_module directory? Another thing is that the construction of safe paths seems to include the "plugins" folder itself (rather than the directory of a specific plugin)... Could be a problem.

Anyway, at this point, I suggest that you 1) try downgrading generator-core's source to tag 3.12.0, 2) if it works, open a ticket on generator-core's bug tracker, then 3) revert generator-core to currently version (this is a security fix, so you should not ignore it) and try to work out a solution.