okular fails to run after latest Xubuntu upgrade

[MR ZenWiz]

On Fri, May 7, 2021 at 1:51 PM MR ZenWiz <mrzenwiz at gmail.com> wrote:
>
> 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

Addendum: atril no longer works, either.

I'm running Xubuntu 20.04.2 with today's update.