Jupyterlab python editor extension?

JupyterLab
,
3

The folding is available by CodeMirror, which can be modified via the Advanced Settings Editor > Text Editor, and might get you closer to what you’re looking for:

{
    "editorConfig": {
        "codeFolding": true
    }
}

I don’t know of a pithy way to get indentation characters to show in codemirror, but there might be something out there that could be wrapped into…

As for LSP-in-lab: there’s jupyterlab-lsp which knows how to work with python-lsp-server. There’s also a longer discussion.