So, at this point only 3 core apps don't support the dark preference yet. Help and Music have pending MRs, while Fonts will likely be the only one to not support it in 42 because of how it does thumbnails.

There are also a few smaller parts like the keyboard layout preview from libgnomekbd. But those will likely remain as is for now. There are also a bunch of apps that use dark UI by default and don't support prefer-light, but we don't expose it in UI atm.