How to add this square to freeCodeCamp challenges editor when typing on the editor?
This was intentionally disabled - snippets and the suggestions, because it does not help campers learn the syntax as well as a more plain text editor.
There is currently no plan to enable such a feature. So, if you would like this, I recommend you code on your preferred editor, and paste the solution, once done.
Hope this clarifies.
I will code without this feature when learning on freeCodeCamp as you said.