XPS 13 sound output Dell U2520D not found

I've a XPS 13 9305 connected to a U2520D via a DP cable. The U2520D is connected to a speaker via aux. This worked fine until today. My system only shows the XPS speakers. The screen works fine. I've done the Dell update, I've installed the new Realtek drivers (11/24). Doesn't show up. The screen is also connected via HDMI to a Playstation. When the PS is on, the sound works fine. Tried the HDMI, screen is found, but the sound output doesn't show up. Even tried downgrading the Realtek drivers, but this gives an error.