12.0 PR: https://github.com/truenas/webui/pull/5433

21.06 PR: https://github.com/truenas/webui/pull/5402

Additional findings:

1. Actual problem is with pixi.js in system folder.

2. Removing all mentions of pixi.js removes the error.

3. It may have something to do with how pixi.js is imported, i.e. I got it running once by importing via "import * as PIXI from 'pixi.js'" vs "import { Container } from 'pixi.js'. I wasn't however able to replicate this for the whole project.

4. Removing pixi-projection didn't help.

5. Updating pixi to latest version within 4 branch didn't help.

6. Disabling aot helps

Going to stop working on this now.
I've added a check that will run after build and verify that build happen correctly.

1. It only happens with build:prod:aot.

2. The offending code mysteriously dissapears if I enable source maps with --source-map, even in build:prod:aot.

3. It is near pixi.js code, but could be something compiler includes to make something work.

4. This is nodejs code, and there is some other nodejs code that is in the build for whatever reason.

Basically the task here is to figure out why we have nodejs code in prod:aot builds. Search for "process.platform" or "NODE_DEBUG".
The same place (but without an issue) can be found by searching for "Arguments to path.join must be strings".

21.06 PR: https://github.com/truenas/webui/pull/5397