Disclaimer, I’m using CarPlay but it behaves the same way you describe. It is different to the behaviour of CarPlay in my previous VW Passat.
Going into the VW Maps there is a setting for auto light/dark, and this does reflect the auto light control that is detected from the sensor in the instrument cluster, i.e when going through dark areas the VW Map will change into dark mode, but only the map.
If I’m using CarPlay it remains on the day setting, this is especially noticeable when driving at dusk. The car turns on the headlights and the VW Map goes into dark mode. But CarPlay will remain on day mode, even though it is set on the phone for auto light/dark mode. CarPlay seems to be controlled by my phone setting of going into dark mode at sunset, as whatever time sunset is, CarPlay and Apple or Google Maps will then go into dark mode.