I would like to have a hierarchical filter that displays for example keywords grouped by the classification tagbox field. You can add a tree view field to your layer e.g here I have added one to the Basic Information field:

[
    {
        "fieldId": "keywords",
        "allowRecursion": false,
        "levels": [
            {
                "fieldId": "classification",
                "allowRecursion": false,
                "levels": []
            }
        ]
    }
]

Then add a Channel Filter for that field. This will display as follows in your Content Browser:

Say I am only interested in the Weather Classification. In this case I can add a Path to the Channel Filter so that I am not displaying the top level of the tree but one of the nodes. To do this I first select Weather in the Content Browser. Once selected I can then search for the path query string in the url that starts with a , in this case ,GZasG6hGZEeHHMCS05NbCg (it’s the List Item ID Base 64 encoded and separated with a ,):

I can then add this to the path field in the Channel filter as follows:

And will end up with the following display in the Filters where it only shows filter items that have a classication of weather: