Thank you - I think I will have to take the plunge and try our Duplicati. As a now retired system architect for many years I like the concept but my programming skills are quite rusty now. I was the leader of a multi-user OS team in the around 1975 1970s. As an aside we supported 70 concurrent text mode users on a Modular one (UK computer) and the memory limit was 256 kilobytes and the largest disk we had was 50 Mbytes!
My background makes me cautious to an extent and I tend to avoid beta software and experimental versions unless I am very close to the development team. If I were not contemplating migrating to Thunderbird I would stick with Cobian which has served me very well for very many years.
I intend to have a test using a W10 virtual machine before finally making up my mind. I have already installed Duplicati but possibly not the version you are recommending.