Hello Nico,
If you intend to display the UTC time, ensure that the DateTime attribute is configured with "Localize: No".
According to the Mendix documentation:
"Utilize non-localized attributes in scenarios where you do not require the time component (e.g., birthdays) or when you want a date to appear identical worldwide."
DateTime values are stored UTC.
When DateTime attribute is localized (default) then;
When DateTime attribute is not localized then;
So my guess is, your attribute is not localized