iOS 18.3.1 side effect — losing Dark app icons on iPhone home page?

I often get up early, before sunrise, and use my iPad & iPhone. I really appreciate apps using Dark mode in their UIs,as well as displaying dark app icons on the home screen. So I noticed right away after updating iOS to 18.3.1, that all the app icons on the home screen & app library were the bright “light” icons instead of “dark” icons.

Incidentally, the iPhone’s home screen wallpaper, icons, and folder backgrounds continued to become dark as usual.

Meanwhile, all the same app icons on all of the family iPads (various generations, all just updated to iPadOS 18.3) changed to dark icons along with the Dark display & brightness.

I don’t yet know if this issue affects many or few iPhone models. Anyone know?