Looks like this is a very recent change. The correct syntax is:

fig = go.Figure()

fig.add_trace(
    go.Chloroplethmap(
        # etc 
        # etc 
        # etc 
    )
)

fig.update_layout(
    map_style="carto-positron",
    map_zoom=3, 
    map_center = {"lat": 37.0902, "lon": -95.7129}
)

Confirmed this works for go.Chloroplethmap() as of April 2025.