Below are the two screenshots in dark mode. Why is background still white? I don’t get it. Looks like a bug

Below are the two screenshots in dark mode. Why is background still white? I don’t get it. Looks like a bug
Well, I just tested it here on my computer with stock installation of public Mojave and the background is dark as expected.
I guess you have customised your home folder background in Finder. Right Click in the white background, open “Show View Options” dialog and double-check that you really have default background set.