The JS Helper script added before your script is in the HTML tree?
If this doesn’t work then this suggests onAuthorized is also not working and thats required for an extension to complete loading and be permitted to be visible.
You also don’t need to cast it to const twitch should be able to use window.Twitch.ext.onContext directly, additionally window.Twitch.ext.onContext is not for the config service it’s for channel/video update data.
Extension config is loaded via window.Twitch.ext.configuration.onChanged