SELECT 'Simple quote''' FROM dual;        -- Simple quote'
SELECT '''Simple quote''' FROM dual;    -- 'Simple quote'
SELECT q'['Simple quote']' from dual;    -- 'Simple quote'  q'[my_string]'

s_date VARCHAR2(10 BYTE) := '12/02/2021';
EXECUTE IMMEDIATE 'SELECT to_date(''' || s_date || ''', ''DD/MM/YYYY'') FROM dual';