Visual Studio code sidebar Vertical guideline (customize sidebar)

It's still not available. I assume you have problem with navigation through this tree when it comes about projects with complex directory structure (for me it's very, very annoying).

Right now I'm using extension seti-cons. It doesn't create vertical line, but adds icons for folders etc. what helps a little bit :)

Here, how it looks like on example project:

It's not perfect, but always something.

And in v1.36 tree indent guides are implemented, see release notes, tree indent guides.

Plus, you can change their color with this colorCustomiztion:

"tree.indentGuidesStroke": "#ff0000"

You can add guidelines with:

"workbench.tree.renderIndentGuides": "always", // Can also be set to "onHover"

You can also change their color with:

"workbench.colorCustomizations": {
    "tree.indentGuidesStroke": "#008070"
},

And if you want to change the indentation width, you can use:

"workbench.tree.indent": 18,

I bring up on GitHub. see that:

Visual Studio code sidebar Vertical guideline (customize sidebar)

and other Issue

Directory tree indent guides in File Explorer