A html file with:

<img src="black.png" id="myImage"/>

and a CSS with:

@media (prefers-color-scheme:dark) {
img#myImage { content: url("white.png"); }
}

The switching of dark or non-dark mode should cause the img tag to load the appropriate image. This does not today happen.

You can see this on a real website on flowee DOT org/index.html (the product logos at the right).

I hope this is a helpful issue report!