Qubes OS by default runs xfce desktop environment. You can also switch to KDE. Qubes team does not develop those environments* and questions related to them are not Qubes-specific. You can find answers in the xfce/KDE documentation and forums. You can find the list of default shortcuts there, too.
If you click on the pen symbol on the right, near the post time, you will see that it was in Feedback category. No problem though, mistakes happen.
*However, Qubes adjusts the environments to improve the UX, see for example this: New Qubes application menu.