SQL> select banner_full from v$version where rownum=1;

BANNER_FULL
--------------------------------------------------------------------------------
Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production
Version 19.22.0.0.0


SQL> select database_role from v$database;

DATABASE_ROLE
----------------
PHYSICAL STANDBY

SQL> select database_role from v$database@primary;

DATABASE_ROLE
----------------
PRIMARY

SQL> desc temp
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 S                                                  VARCHAR2(100)

SQL> select dbms_flashback.get_system_change_number@primary from dual;

GET_SYSTEM_CHANGE_NUMBER
------------------------
              3.4359E+11

SQL> alter session enable adg_redirect_dml;

Session altered.

SQL> desc temp
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 S                                                  VARCHAR2(100)

SQL> insert into temp values('bla');
insert into temp values('bla')
            *
ERROR at line 1:
ORA-16397: statement redirection from Oracle Active Data Guard standby database
to primary database failed

primary is a database link from the physical standby (opened read-only) to the primary.
The insert succeeds when we omit the call to dbms_flashback.get_system_change_number@primary

Is it a bug or a feature ?
If feature: what exactly is featured here ?