added whatsnew for pandas-dev#24265

Author: jbrockmendel

doc/source/whatsnew/v0.24.0.rst

@@ -1367,6 +1367,7 @@ Datetimelike
 - Bug in :attr:`Series.dt` where the cache would not update properly after an in-place operation (:issue:`24408`)
 - Bug in :class:`PeriodIndex` where comparisons against an array-like object with length 1 failed to raise ``ValueError`` (:issue:`23078`)
 - Bug in :meth:`DatetimeIndex.astype`, :meth:`PeriodIndex.astype` and :meth:`TimedeltaIndex.astype` ignoring the sign of the ``dtype`` for unsigned integer dtypes (:issue:`24405`).
+- Fixed bug in :meth:`Series.max` with ``datetime64[ns]``-dtype failing to return ``NaT`` when nulls are present and ``skipna=False`` is passed (:issue:`24265`)
 
 Timedelta
 ^^^^^^^^^