Gimp stopped working - complaining about RANDR extension

As of this morning, gimp has stopped working for me on my 11.1 install.
It complains:

Xlib: extension “RANDR” missing on display “:0.0”.

when I try it from the command line.

I’m sure it worked yesterday!

It reports it’s version as
GNU Image Manipulation Program version 2.6.2

and has been installed as a package from wherever these things come from ( the official distribution source, I guess)

Sure, other things occasionally squawk about RANDR missing, but I would have thought it was not really important (at least on a desktop)