I think this is fixed in Mendix 8.9, i see something in the release notes related to this:
I checked it in an 8.12 project and there you have a ‘custom’ option to change this. Maybe you can upgrade the project to 8.12?
Ah sorry my bad, reacted to fast did not check complety. The drop-down reference indeed does not give this option. What you can do:
- Change the date-time formatting throughout the application. Settings > Languages > double click on the correct language and set the custom date and/or time format
- If you only want to change this only for this drop-down, create either a helper entity with a string formatted date or an extra attribute with the correct formatted date.
- Create an idea on the idea forum to let Mendix add this to the possibilities: https://forum.mendix.com/link/ideas