Issue / limitation pointed out by Dmitry here: https://bugs.kde.org/show_bug.cgi?id=444535#c1 who suggested I file a separate bug report about it. I can provide repro steps if necessary.

Actual behavior:

If you make a keyboard shortcut in the khotkeys system setting UI, and that shortcut has a window filter, if you don't actively select a bullet to indicate the type of window you want to match, no windows are matched.

Expected behavior:

When creating a filter, if you don't choose a specific type of window to match, most users would expect that part of the filter to be inactive and all window types to be matched. Presumably the user wants to filter on something else, like window title or role.

Suggested fix:

Simply changing the behavior to match all windows if no window type is selected would still not be ideal from a UI perspective. That's because the user is not given any way to actively select "all windows" for the type filter, and if the user accidentally or deliberately selects a type filter, there's no way to undo that and go back to matching all windows (because of the way radio buttons work in QT).

So the best solution here is to add an additional radio button that says "All windows" or something similar, and have that selected as the default option in the filter widget UI.