Comment # 3 on bug 1166496 from Josef Wolf

> PS: I meanwhile found https://bugs.kde.org/show_bug.cgi?id=369137, which seems to be about the same problem.

Yes, it seems to be about the same problem. But it suggests that the problem
appears only whe using kodi, which is not true.

> According to the comments, this cannot be fixed from the KDE/Plasma side on X11 (and seems to work fine on Wayland).

Yes. But I fail to understand that. As I mentioned, the problem does not occur
wit e.g. gdm. Thus, there must be a way to do it properly.

> The recommendation is to use Plasma's "Switch User" functionality to switch to a different session (which should lock the screen immediately) instead of Ctrl+Alt+Fx.

The "switch user" functionality suffers from the same problem. So this is not a
workaround.