As you can see in the above pictures I am using the Fedora theme and you can see the dynamic wallpapers configuration. Also night light is enabled (I do not think it is related to that but might useful).
All other programs are displayed in light mode (bright appearance).
However my wallpaper is in night mode. I have the same problem with other day/night wallpapers too.
It happened after I updated to Plasma 6.5.1 from 6.4
I have not enable auto switch from light to dark.
It’s because Fedora Plasma Theme is a Dark Theme while the Application Theme is a Light one - the wallpaper follows the Plasma configuration. You can just set the wallpaper to be always light version to fix that.
But if I set that to always use light variant If I enable a dark theme the wallpaper will be light.
I should know that if it is a bug or a new feature in Plasma to align myself with it.
As always, this question is often impossible to answer 
However, I ended up setting mine separately (or by time) and when it doesn’t suit then I just over-ride it.
CtrlShiftD when desktop is selected (MetaD)
