Hi Christian,
the text widget has no logic to format date strings. If you want to do this with a widget you have to use a date related widget like for example the DateTimePicker. DateTimePicker has a property displayFormat where you can specify a format with “dd.MM.yyyy”. The DateTimePicker is an input widget. That means you have to diasble “editable”, If you want it read only.
Another approach would be to format the date yourself with good old javascript. I would do that client side where you could use a js package like “moment” https://momentjs.com/docs/#/displaying/format/
Look at “Localized formats” to get the correct format type for your users location.
After formatting your date with moment js you can display it with a simple text widget.