Using a touchpad (on laptop or using external touchpad), the system setting "Invert scroll direction (Natural scrolling)" (for touchpad) is not respected in system tray widget for sound volume control (via the "audio volume" and "media player" icons). More precisely, enabling natural scrolling do not change the behavior of scrolling over the system tray widget, which continue to respond as if the setting was disabled.
Thank you for the bug report! This is intentional behavior, see e.g. the already existing report which I'm marking this as a duplicate of. This matches natural scrolling as implemented on touchscreens - to move a scrollable view (like a web page) down, you move your fingers up, as if you're moving a piece of paper. But to move a slider, you do not move your finger down to move it up, that would be unnatural - you're not moving the background, but the element itself. These widgets work the same way, as they're based around sliders. See also the original discussion in https://bugs.kde.org/show_bug.cgi?id=442379 *** This bug has been marked as a duplicate of bug 478146 ***
Thanks for the answer. I understand it is the intended behavior for touchscreens, but as a touchpad user it feels off (I repeat the gesture for scrolling a page as a reflex). Having the option to choose would be fantastic (or separate the touchscreen/touchpad behavior).