Currently the only way to change that sound to something else is to replace the file /usr/share/sounds/freedesktop/stereo/audio-volume-change.oga with the user desired sound file. This is not intuitive at all. It would be better if there was an option is System Settings to change the sound effect easily like various notification alert sound effects.
Indeed, this would be nice. I've wanted it myself.
In principle this is not that hard. In volumefeedback.cpp, you just need to make the name of the sound configurable, and then add a UI to let users pick from a set of pre-curated options (with perhaps an option to add your own custom sound). For example:
/usr/share/sounds/Oxygen-Window-All-Desktops.ogg = "Hum"
/usr/share/sounds/Oxygen-K3B-Finish-Success.ogg = "Piano"
/usr/share/sounds/freedesktop/stereo/audio-volume-change.oga = "Pop"
/usr/share/sounds/freedesktop/stereo/bell.oga = "Droplet"
The logical place for this UI would be in the KCM, but then it's awkward because all the other global settings currently live in the applet, but that's inappropriate and they *should* live in the KCM because these settings are not applet-specific. But doing that is a ton of work. We'd have to:
1. Move the UI into the KCM and write necessary backend code for it
2. Write a singleton settings object that can act as a bridge between the KCM and all plasma-pa applets
3. Write a kconf update script to migrate the settings away from the applet and into something backed by kconfig
Too overwhelming; giving up for now. Maybe I'll revisit this later.
I agree that these settings should reside in kcm. As a new user I had no idea that I could disable the feedback sound by right clicking the applet instead of finding it in system settings. This is a very important toggle that should be in system settings and thus searchable from anywhere. I can understand that it's too much work moving all these settings to kcm but these basic usability improvements I think should be important for upcoming steam deck adaptation.