It's fairly unintuitive that Plasma applets are capable of doing things like handling global shortcuts, such that removing or disabling the applet disables the shortcut. There are various legitimate use cases for when a person might not want to use an applet, but still wants the global shortcut functionality it provides. An example would be wanting to disable the Media Player applet because you never use it, but still wanting for global media shortcuts to work. Presumably the functionality in question would be handled by a kded module, or by Plasma itself. This is an umbrella bug/metabug that tracks individual instances of where users have requested this or been tripped up by the lack of it.
I somewhat agree all applets should be super thin front ends, rather than any place where there's any "business logic". But this isn't always trivial. For klipper the applet is where the data is stored - I can't think of a viable way to solve that without /massive/ new infra. Volume has some options, especially if we gain a plasma specific pipewire controller that we'll need anyway. Note that it does introduce a UX problem as well as solving one. If you remove the media applet it's because you don't want to use said thing, but you haven't really disabled it.
I want to use global media control *shortcuts*, but I don't ever use the Media Player *applet*. I'd like to disable/remove the former without disabling/removing the latter.
That is achievable by setting the applet to Hidden.
That's what I've done, but it's not quite good enough because it still appears in the expanded view.
Invent issue: https://invent.kde.org/plasma/plasma-desktop/-/issues/113