Mike, thanks for your continued help in this!
You said:
"I don't understand the subtle differences between your underlined alternatives, and a lack of attachment does not help"
I did try to include an image but plainly I got it wrong somehow. I've tried to include it again.
This is what I do:
Select an individual, select the 'Media' tab, click on the green + sign.
Select 'Insert from file' , browse to the folder, select jpg in the drop down and click on a jpg image
So far all is as it would be in Win 10 but from here it all goes wrong as I get the following:

- Screenshot.jpg (18.05 KiB) Viewed 7461 times
The box 'Save file' is always empty in Linux whereas in Win this box will show the filename to be "inserted". So, although I can navigate to the wanted folder and filename this box doesn't pick it up for some reason. I have tried having the image in various folders in various places but the result is the same.
I have tonight tried an uninstall/reinstall under Wine specifying Win7 in case I did something wrong before but there was no change.
You also wrote:
"Looking back at your original posting, the error message appears to be referring to the file "." which is a Unix shortcut to the current folder"
If you look closely at the error ("Media insert failed. Unable to copy file "".") you will see that it ends ""." or expanded (" " .")
Removing the first and last quotes gives you: Media insert failed. Unable to copy file "".
So you can see it represents a Null entry and not a . (dot) entry - sorry about the confusion.
This evening I have also tried to export a ged file and it fails, nothing at all is saved in the selected location. However, text changes made to my own project
are saved - so now I'm really at a loss.