The New Map Viewer does not have the ability to configure the date/time fields for non-American date/formats e.g. 26/04/2021 not 04/26/2021 like the majority of the world views dates.
These are the only options,
whereas in the MapViewer Classic these were the options:
Edit:I'm adding the request for Scene Viewer as well. We are an Australian Local Government Agency and it would be really great to view dates in an Australian format. I have seen other ideas that say utilise regional system settings that could possibly work in this scenario. Not everyone is familiar with how to read dates outside of the regular Australian format dd/mm/yyyy. it would be great to see additional options added or for the option to use a regional system setting.