Addendum to the problem of exporting final images from darktable:
if I reselect the image and try export again, the footnote (bottom left., just below "lua scripts installer" in lighttable) now has two lines -
"exporting 1/1 to file on disk
This suggests the two actions (export button clicks) are sequential actions, but the first one is stuck, to the next one on the stack sits without actions......
This is really frustrating , as I am new to digital photography, want to get images edited and post-produced, exported and printing.... but this is 'broken' :-(
thanks in advance for any help.