DateTimes are stored in UTC behind the scenes and are translated to local time in your application as necessary.
From the documentation: https://docs.mendix.com/refguide/date-and-time-handling/
“Coordinated Universal Time (UTC): The platform stores all dates in the UTC time zone. This is a time standard that is often used in servers to provide an unambiguous date format. It does not change with a change of the seasons (DST). Every time a date or time is presented to the user it is localized to the time zone of the client unless specified differently.”
There is also a DateTime FAQ that gives some more information.
Hope this helps.