Oracle 18c

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create or replace package p as

type result_str is table of varchar2(100);

function unpack_list(
  string_in in varchar2
) return result_str;

end p;
/
create or replace package body p as

function unpack_list(
  string_in in varchar2
) return result_str 
is
  result_rows result_str;
begin
  
  with temp_table as (
  SELECT distinct trim(regexp_substr(string_in, '[^,]+', 1, level)) str
  FROM (SELECT string_in FROM dual) t
  CONNECT BY instr(string_in, ',', 1, level - 1) > 0)
  
  select str bulk collect into result_rows from temp_table;
  
  RETURN result_rows;
  
end;

end p;
/
select * from p.unpack_list('one1, two2')
ORA-00902: invalid datatype

declare
  l_result_str p.result_str;
begin
  l_result_str := p.unpack_list('one1, two2');
  for i in 1..l_result_str.count loop
    dbms_output.put_line(l_result_str(i));
  end loop;
end;
/
1 rows affected

dbms_output:
one1
two2