As How to set display to disable when locked? explains:
In Plasma 6, you can configure the system so that the display turns off at the same time when the screen locks, so this would be the expected way to do that.
In Plasma 5, the feature is not officially supported.
@ngraham, it’s only one example (which was aforeexplained in the original thread, although I’m thankful anyway) because I couldn’t think of any others I intend to use currently. However, it’s a rather brittle system - wouldn’t it be better to be able to choose which actions to be invoked and in what order, rather than be limited to that specific combination or merely one action? Such a system seems like its versatility would ultimately make it more maintainable.
Sure, such a thing could exist, but could result in a more complicated UI for a fairly niche set of features. Trade-offs.
To expand the potential use cases a little more, the Screen Locking settings module also has a checkbox to lock on wake-up. So that’s another stackable combo that’s already possible with current Plasma.
I’d think that for unlimited flexibility, we’d probably want to allow for custom scripts on sleep/wakeup or button press instead of changing the already complex UI to allow multi-selection.