Looks good.

There's one issue I want to point out that I dealt with, is that other instances of the widget won't be in the "raised" state (eg: other screens).

Example: https://streamable.com/go1u7

My solution was:
https://github.com/Zren/plasma-applets/blob/master/org.kde.plasma.volumewin7mixer/package/contents/ui/MixerItem.qml#L372-L379

property int volume: PulseObject.volume
onVolumeChanged: {
    ignoreValueChange = true;
    if (!mixerItem.isVolumeBoosted && PulseObject.volume > maximumValue) {
        mixerItem.isVolumeBoosted = true;
    }
    value = PulseObject.volume;
    ignoreValueChange = false;
}

There's one issue I want to point out that I dealt with, is that other instances of the widget won't be in the "raised" state (eg: other screens).

Multiple instances have also separate settings, so I don't see this as an issue.

However, it is possible that other apps raise volume above 100% (eg. vlc) and you won't be able to change it (only lower down to maximum - 100% or according to applet settings), so this should be taken care of (raise temporarily as long as the value is above maximum). But this should go in another commit.

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