For any that are interested. The connectivity of cameras via USB to macs running Catalina was causing some problems for various cameras and software. With the latest (January) release of EOS utility 3 - which installs EOS utility 2 for older cameras it all seems to work OK. I updated EOS utility (from the 5Ds camera page) and connected my 1Div - the launcher correctly launched EOS utility 2 which connected the camera and downloaded OK. The history (apparently) was that an update to Catalina broke the December version of EOS utility. Since that time there have been new versions of Catalina and the Canon software (including DPP 4). Catalina only runs 64 bit applications and has much tighter security, e.g. apps need explicit permission to access folders, network etc. This has caused numerous issues for devices that connect by USB or wireless.