It changes with light/dark mode. If you want changing wallpapers use something like https://github.com/saint-13/Linux_Dynamic_Wallpapers
KDE
KDE is an international technology team creating user-friendly free and open source software for desktop and portable computing. KDE’s software runs on GNU/Linux, BSD and other operating systems, including Windows.
Plasma 6 Bugs
If you encounter a bug, proceed to https://bugs.kde.org/, check whether it has been reported.
If it hasn't, report it yourself.
PLEASE THINK CAREFULLY BEFORE POSTING HERE.
Developers do not look for reports on social media, so they will not see it and all it does is clutter up the feed.
How does dark & light mode change on its own? The Bazzite reference I made was I believe I remembered the background changing depending on the time of day or maybe it had a button to switch the modes in the panel with easy access (can't quite remember). On Kinoite I have the screen set to red light automatically at a certain time but the theme doesn't change to dark with it. Is this a possible feature with Plasma?
There is in GNOME
Know idea about kde ... https://invent.kde.org/plasma/plasma-workspace/-/issues/59
Youcan always write a script that runs at dawn and set and change the theme.