What is the shortcut to show the Red Overlay in Mask on German Keyboard (not Q)

@melanied95 

I think you said you want to show the overlay for the mask and not for QuickMask.

If that's true, show us your Channels panel. The shortcut for each color channel and alpha channel are displayed on the right. You can click the eyeball for the alpha channel or use the keyboard shortcut.

If it's not true, please clarify and show the screenshots that C.P. asked for.

Could you please post screenshots taken at View > 100% with the pertinent Panels (Toolbar, Layers, Channels, Options Bar, …) visible? 

I'd hope that the tool tip when hovering over the icon in the toolbar would offer guidance.

Is "Toggle layer mask on/off as rubylith (layer mask must be selected)" what you mean?

• https://helpx.adobe.com/photoshop/using/default-keyboard-shortcuts.html#keys_for_viewing_images

On German keyboards, it's the "<" key.

• https://helpx.adobe.com/de/photoshop/using/default-keyboard-shortcuts.html#keys_for_viewing_images

("Ebenenmaske als Farbüberzug ein/aus (Ebenenmaske muss ausgewählt sein)")