How/where exactly did you run that piece of code? I tested it on TOAD and SQL*Plus in Oracle 11g.
Sample table:
SQL> CREATE TABLE s_accnt_att
2 (
3 row_id NUMBER,
4 par_row_id NUMBER,
5 file_name NUMBER,
6 file_ext NUMBER,
7 conflict_id NUMBER
8 );
Table created.
Procedure:
SQL> SET SERVEROUTPUT ON;
SQL>
SQL> DECLARE
2 l1 INTEGER;
3 BEGIN
4 EXECUTE IMMEDIATE q'[
5 begin
6 execute immediate ' CREATE INDEX S_ACCNT_ATT_P1 ON S_ACCNT_ATT ( ROW_ID ) PARALLEL 4 ';
7 execute immediate ' CREATE INDEX S_ACCNT_ATT_U1 ON S_ACCNT_ATT ( PAR_ROW_ID , FILE_NAME , FILE_EXT , CONFLICT_ID ) PARALLEL 4 ';
8 execute immediate ' select 1 from dual '
9 into :l1;
10 end;
11 ]'
12 USING OUT l1;
13
14 DBMS_OUTPUT.put_line ('L1 = ' || l1);
15 END;
16 /
L1 = 1
PL/SQL procedure successfully completed.
SQL>
Seems to be OK.
As your target database is 19c, I tried it there as well; no problem.
SQL> select banner from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
SQL> DECLARE
2 l1 INTEGER;
3 BEGIN
4 EXECUTE IMMEDIATE q'[
5 begin
6 execute immediate ' CREATE INDEX S_ACCNT_ATT_P1 ON S_ACCNT_ATT ( ROW_ID ) PARALLEL 4 ';
7 execute immediate ' CREATE INDEX S_ACCNT_ATT_U1 ON S_ACCNT_ATT ( PAR_ROW_ID , FILE_NAME , FILE_EXT , CONFLICT_ID ) PARALLEL 4 ';
8 execute immediate ' select 1 from dual '
9 into :l1;
10 end;
11 ]'
12 USING OUT l1;
13
14 DBMS_OUTPUT.put_line ('L1 = ' || l1);
15 END;
16 /
L1 = 1
PL/SQL procedure successfully completed.
SQL>
Therefore, maybe it is about your migration tool (which one is it) that doesn't recognize the q-quoting mechanism. If that's so, don't use it and double single quotes instead:
SQL> DECLARE
2 l1 INTEGER;
3 BEGIN
4 EXECUTE IMMEDIATE '
5 begin
6 execute immediate '' CREATE INDEX S_ACCNT_ATT_P1 ON S_ACCNT_ATT ( ROW_ID ) PARALLEL 4 '';
7 execute immediate '' CREATE INDEX S_ACCNT_ATT_U1 ON S_ACCNT_ATT ( PAR_ROW_ID , FILE_NAME , FILE_EXT , CONFLICT_ID ) PARALLEL 4 '';
8 execute immediate '' select 1 from dual ''
9 into :l1;
10 end;
11 '
12 USING OUT l1;
13
14 DBMS_OUTPUT.put_line ('L1 = ' || l1);
15 END;
16 /
PL/SQL procedure successfully completed.
SQL>