“This Week in Plasma” brings the news that Plasma 6.5 will have automatic day/night theme switching, that you can choose which Global Themes to show on the Quick Settings page, and that you can set dynamic wallpaper coloration to be based on the background color scheme or the time of day, or always light, or always dark.
https://blogs.kde.org/2025/08/02/this-week-in-plasma-day/night-theme-switching/
Hallelujah!