okular fails to run after latest Xubuntu upgrade

[MR ZenWiz]

The Xubuntu Software Updater ran today and updated some stuff (not
sure exactly what - I wasn't watching that closely).

After the update, my okular fails to run with the following message:

$ okular
qt.qpa.xcb: could not connect to display
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even
though it was found.
This application failed to start because no Qt platform plugin could
be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl,
offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl,
wayland-xcomposite-glx, xcb.

Aborted (core dumped)

I purged the app and re-installed it, same error.

Can anyone tell me what happened?  I use the okular and k3b apps, but
never with this bad a result.

Thanks.

Mark