Both on EBI03 (MariaDB 10.5.13) and EBI01 (MariaDB 10.3.16) the following bug was found on Columnstore tables:
an insert into a datetime field of '0000-00-00 00:00:00' stores it this way,
BUT an UPDATE on datetime field of '0000-00-00 00:00:00' stores it as <null>
whereas on InnoDB tables in both cases '0000-00-00 00:00:00' is stored.
See the attached SQL.
Note: the SQL_MODE options STRICT_TRANS_TABLES, ALLOW_INVALID_DATES, NO_ZERO_DATE, NO_ZERO_IN_DATE might have an impact.
However, on the same session with the same set of SQL_MODE settings, in any case both engines should behave the same.