SUMMARY
Updated to KDE neon (Testing) shortly after the Plasma 6.3.1 release, and noticed that my monitor's DDC/CI hardware brightness settings are inaccessible.

Plasma will still provide software brightness instead, but this can only dim the screen, it won't be able to raise my brightness from 30 to 70 on the monitor itself. Furthermore, software dimming will necessarily reduce the available color gamut because if you cap the maximum pixel color value, you have fewer colors available overall.

Installing the `ddcutil` package will fix this. Strictly speaking it should already work with the (preinstalled by default) libddcutil library / `libddcutil4` package, however the udev rules that provide the required permissions are part of the `ddcutil` package so libddcutil by itself is neutered on Debian-based systems.

STEPS TO REPRODUCE
1. Connect external monitor
2. Log into Plasma session
3. Click "Brightness and Color" applet icon in the system tray

OBSERVED RESULT
There is a brightness slider for your external monitor, but it's separate from the monitor's OSD menu. It will start out at 100% and can only dim the monitor.

EXPECTED RESULT
There is a brightness slider for your external monitor, and after moving the slider, the monitor's built-in OSD menu will show the same percentage as what you configured using the applet.

SOFTWARE/OS VERSIONS
Operating System: Ubuntu 24.04.2 LTS (Noble Numbat)
KDE Plasma Version: 6.3.2
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.2
Kernel Version: 6.11.0-17-generic (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 7840U w/ Radeon  780M Graphics
Memory: 30.7 GiB of RAM
Graphics Processor: AMD Radeon 780M
Manufacturer: Framework
Product Name: Laptop 13 (AMD Ryzen 7040Series)
System Version: A7

ADDITIONAL INFORMATION
Installing the `ddcutil` package (to fix this) will additionally draw in the package dependencies `i2c-tools`, `libi2c0` and `read-edid`.