Things are a quite a bit more complicated than that. This is not related to your editor, VS Code is an excellent choice.
Discourse is a MVC single page app that uses EmberJS on the front end and uses Routes, Models, Controllers and Templates.
Changing only the Templates is usually not sufficient.
It would be really good for you to do some reading into EmberJS.
But for example, part of the reason there is no functionality, is because the Controllers are different.
Here are all the Controllers for this part of the javascript end of the app:
The slight complication here is sometimes Components respond to actions, as well as Controllers.
On top of that you might have to worry about what model is presented to each of these different Routes.
The preferences Routes are here with prefix preferences:
It gets more complex than that too, as the data that Ember sees is almost always originally delivered by the back end and so affected by the Rails Routes, Controllers (and often Models) and Serializers at the back end. See https://guides.rubyonrails.org/