Audio devices disappearing?

My monitor is plugged into an Nvidia 4090 via a DP cable.
I use the audio channel of this DP connection, and this always worked fine until a few months ago: The audio device disappeared.
In Device Manager it used to show up under 'Audio inputs and outputs'.
Using a HDMI cable also doesn't make the audio device reappear.

I also have a USB headset, and a few weeks after the problem above, this audio device also disappeared!
The headset is still detected under 'Sound, video and game controllers' but I cannot select it in the windows audio options.
Same here, it used to show up under 'Audio inputs and outputs'.
Now when I plug it in, there is a 'USB Composite Device' which appears under 'Universal Serial Bus controllers' but that's it.

The headset does work in my laptop, so there must be something wrong with my PC.

I tried reinstalling the Nvidia driver, the headset's driver and the onboard Realtek audio device's driver but nothing helps.