SUMMARY
When changing the volume of an app playing media (such as Elisa or VLC) via the "Media Controller" > "Media volume up" / "Media volume down" shortcuts, the amount that the volume changes by is unaffected by the "Volume change step" audio setting.

STEPS TO REPRODUCE
1. Change the "Volume change step" setting under "Sound" > "Configure Volume Controls..." > "Volume change step" in System Settings from 5% to some other value.
2. Also in System Settings, setup keyboard shortcuts at "Keyboard" > "Shortcuts" > "Media Controller" for either / both "Media volume up" and "Media volume down".
3. Open an app that plays media, like Elisa or VLC, and change its volume using the shortcuts.

OBSERVED RESULT
The application's volume steps at 5% (I think the default volume stepping setting value).

EXPECTED RESULT
The application's volume steps at a value equal to the one set by the user at the system level (configured in reproduction step 1. above).

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Arch Linux (Kernel 6.15.2)
KDE Plasma Version: 6.3.5
KDE Frameworks Version: 6.14.0
Qt Version: 6.9.1

ADDITIONAL INFORMATION
When adjusting the volume using the mouse's scroll wheel on the "Media Player" widget, the volume steps at values that equal the value set by the user at the system level (configured in reproduction step 1. above).

I also do not have the kmix app installed, I'm using plasma-pa with pipewire (including pipewire-pulse) for my audio.

Here is a video of me reproducing the issue: https://drive.google.com/file/d/1h6oroEUNxnfsaQlG-X9tJ9JdV7uqv7Xx/view?usp=sharing