In T64782#681963, @Brecht Van Lommel (brecht) wrote:

These preferences are specific to the keymap, as they depend on the specific mapping of each. If you use a custom keymap, these are indeed not available.

It's confusing/weird that the Delete option of the menu doesn't work but the rest of options does. At first I though that it was not possible to delete channels until I pressed the Del key.
I think the menu option should delete the channels as the Del key.