Date time, always a pain in the @$$
Take a look at this learning path for more background on how DateTimes are handled
I have this issue too and a quick search on the forum learns that many people face this issue. For example see https://forum.mendix.com/link/questions/95717. I think the only solution is to add a text attribute and keep a textual copy of the DateTime value there. You can use formatDateTime for that if you are sure that the microflow is executed by a user in the right time zone, otherwise you can use a java action for that.
The java code that I use is:
TimeZone tz = TimeZone.getTimeZone(timeZone);
SimpleDateFormat sdf = new SimpleDateFormat(pattern);
sdf.setTimeZone(tz);
String result = sdf.format(date);
I embedded this code in a java action "FormatDateTimeWithTimeZone” with parameters: