Your documentation is probably outdated about ngx-highlightjs

[MurhafSousli]

Your main.ts file is different because you are using the traditional angular module, the example shows how to bootstrap in standalone component mode.

Just import the module in your app.module.ts and it will work fine.

main-custom.ts is just a file name on the gist I use to show example code (custom config in main file), each file on the gist must have a name but its irrelevant to the docs.