Capture click in plotly choroplethmapbpx

I've been trying for some days to create a callback responding to user interaction within ipywidgets and plotly.graph_objects.choroplethmapbox. The use case is to split an existing river subcatchment polygon in two at a point in the river, so I need both the coordinates of the click and the polygon that was selected (the construction of the extra subcatchment boundary is handled elsewhere). Is this possible within the graph_objects.choroplethmapbox ipywidget? (I jumped to plotly from ipyleaflet because I could't get client-side hoverinfo to work). With go.choroplethmapbox the map displays, hoverinfo works nicely, and registering the callback goes without error, but the callback is simply not being called. Windows 10, Python 3.11, shiny 0.9.0, shinywidgets 0.3.2, ipywidgets 8.1.2, plotly 5.22.0. Some answers to this has been given at the py-shiny Discord channel, question repeated here on request.