Thank you for offering to help.  The problems are in the French version of QuickBooks Online.  My settings clearly state a date format of dd/mm/yyyy.

However, the system mixes the format up:

• the list of invoices on the screen shows mm/dd/yyyy;
• in customer's details the list of their transactions shows in dd/mm/yyyy;
• bank transactions show as dd/mm/yyyy.

But it does seem that either the US and/or UK version is updating the code in the French system (despite it being discontinued) and some improvements have been made across the board (ie, in other areas that were ridiculously impossible, such as the online payment option not showing/available on recurring automatic invoices).  Improvements are welcome, though too late.

Thank you.