Turn on or off rendering of categories in a QGIS categorized layer

rendercontrol.py

def rendercats(searchstring):
    layer = iface.activeLayer()
    renderer = layer.renderer()
    categories = renderer.categories()
    new_renderer = QgsCategorizedSymbolRenderer(attrName=renderer.classAttribute())
    for cat in categories:
        value = cat.value()
        if value is None:
            cat.setRenderState(False)
        else:
            m = re.search(searchstring,value)
            cat.setRenderState(m is not None )
        new_renderer.addCategory(cat)
    layer.setRenderer(new_renderer)

Error "AttributeError: 'NoneType' object has no attribute 'renderer'" means that no layer is currently selected. Click the selected layer and rerun

Searchstring can be any regex. The simplest will just be a string, then if that string with matching case is in the categorization value, that category will be rendered. Start the string with ^ to anchor the search to the start, end with a $ to anchor it at the end. Search python re for other possibilities.

Layer has to be rendered with Categorized Symbology