Recent update to Plasma 5.26.3 level in Leap 15.4 via yast resulted in a
seriously unworkable desktop.  The desktop and panel appear to come up OK, but
then, among other things:

- No window titlebars and no means of moving windows either with mouse or from
keyboard

- No virtual desktops - attempt to re-establish them via System Settings
results in error "requesting information from the compositor" 

- Click-to-focus doesn't work.  Unresponsive.  Can't grab windows by any means.
 Application shutdown limited to Ctl-Q

These behaviours and others appeared after the above update on a running system
a couple of days ago.  I've also restored the system from a prior full system
backup and applied the update again.  Same result.