isValidDatetimeUtc static method
Returns true if str parses to a UTC date/time.
Unlike DateTime.parse, an unparsable, null, or empty str returns
false instead of throwing.
Implementation
static bool isValidDatetimeUtc(String? str) {
if (str.isNullOrEmpty) return false;
final dateTime = DateTime.tryParse(str!);
return dateTime != null && dateTime.isUtc;
}