I agree down loses it’s insulation properties to a degree but modern down jackets coat the down to help it avoid saturation with water.
One or two brands are using treated hydrophobic down – Berghaus for example, and Rab – most don’t, but generally the shell fabrics will have some sort of DWR treatment so they should cope with light showers okay, but eventually they’ll leak at the seams.
Untreated down loses its ability to loft if it gets properly wet and then needs careful drying with agitation to recover its loft afterwards, water-repellent down dries faster and recovers more fully without special drying. Bt generally, wet down, doesn’t keep much of its insulation properties when wet through, but if its just the shell getting damp it’ll be okay.
If you’re looking at using down regularly in conditions where it might get wet, you’re probably better off with a synthetic alternative. Primaloft is very good, but there are others too.