Running JupyterLab version 3.0.0 and would like to enable code folding (collapse classes, functions etc in Python). I have followed the instructions in this Jupyter Lab github post:

Under Settings / Text Editor, I have these User preferences (right pane):

{
    "editorConfig": {
        "lineNumbers": true,
        "codeFolding": true
    }
}

And I do not see any triangles appearing on the left side of the cells. What else do I need to do in order to enable code folding?

For abundance of clarity, this question pertains to JupyterLab specifically.

Those instructions are specifically for the text editor, not the notebook interface.

Try this instead, in Settings / Notebook:

{
    "codeCellConfig": {
        "codeFolding": true
    }
}

If you want to enable code folding for Markdown or raw cells, see markdownCellConfig and rawCellConfig respectively.