Some components that are disabled don't show this without theming. An example being knobs, see the tension knob in the Automation Editor. It's only enabled with the cubic hermite progression and disabled for the other progressions but there is no visual indication that it's disabled other than that it's immobile.

I think all changes needed may be in style.css. We have some theming of disabled components already. See the Edit->Redo menu entry when there are no undone actions.

@LMMS/artwork-team

Edit: New commit with disabled knobs (#4378)...