Hello @mglraimundo
The default Material design has a built-in a collapsible sidebar. I believe you could simply add a DropDown component into the built-in sidebar and you would have something similar to the example you have shown.
I think you are asking how to add a thin horizontal line. This can be done by creating a custom HTML component and adding a horizontal rule to it (e.g., <hr>). Then, you can drag that component into your sidebar.
If I am misunderstanding something, please clarify and ideally show what you have tried so far if possible.