Two anonymous plsql blocks checking those tables (starting with "DBA_HIST_" in SYS schema of oracle database) returned line is 0.

plsql_dynamic_cursor.sql

SET SERVEROUTPUT ON;

DECLARE
  v_sql        VARCHAR2(200);
  v_tablename  VARCHAR2(50);
  tab_num      NUMBER;
  v_ref_cursor SYS_REFCURSOR;
BEGIN
  OPEN v_ref_cursor FOR
  SELECT table_name
  FROM dict
  WHERE table_name LIKE '%DBA_HIST_%'
  ORDER BY 1;

  LOOP
    FETCH v_ref_cursor INTO v_tablename;
    v_sql := 'SELECT COUNT(*) INTO tab_num FROM ' || v_tablename.table_name;
    EXECUTE IMMEDIATE v_sql;
    IF tab_num = 0 THEN
      DBMS_OUTPUT.PUT_LINE('The lines of ' || v_tablename.table_name || ' has been returned 0.');
    END IF;
    EXIT WHEN v_ref_cursor%NOTFOUND;
  END LOOP;
  
  CLOSE v_ref_cursor;
END;
/

DECLARE
*
ERROR at line 1:
ORA-00905: missing keyword
ORA-06512: at line 18

-- The updated version after replied to me on https://www.freelists.org/post/oracle-l/Why-these-two-methods-using-cursor-to-acquire-table-name-and-then-using-this-table-name-to-select-its-returned-lines-is-always-encoutered-a-weird-error,1.
-- on Oracle-L with FreeLists.org.

SET SERVEROUTPUT ON;

DECLARE
  v_sql        VARCHAR2(200);
  v_tablename  VARCHAR2(50);
  tab_num      NUMBER;
  v_ref_cursor SYS_REFCURSOR;
BEGIN
  OPEN v_ref_cursor FOR
  SELECT table_name
  FROM dict
  WHERE table_name LIKE '%DBA_HIST_%'
  ORDER BY 1;

  LOOP
    FETCH v_ref_cursor INTO v_tablename;
    v_sql := 'SELECT COUNT(*) FROM ' || v_tablename.table_name;
    EXECUTE IMMEDIATE v_sql INTO tab_num;
    IF tab_num = 0 THEN
      DBMS_OUTPUT.PUT_LINE('The lines of ' || v_tablename.table_name || ' has been returned 0.');
    END IF;
    EXIT WHEN v_ref_cursor%NOTFOUND;
  END LOOP;
  
  CLOSE v_ref_cursor;
END;
/

    v_sql := 'SELECT COUNT(*) FROM ' || v_tablename.table_name;
                                                    *
ERROR at line 15:
ORA-06550: line 15, column 53:
PLS-00487: Invalid reference to variable 'V_TABLENAME'
ORA-06550: line 15, column 5:
PL/SQL: Statement ignored
ORA-06550: line 18, column 59:
PLS-00487: Invalid reference to variable 'V_TABLENAME'
ORA-06550: line 18, column 7:
PL/SQL: Statement ignored

-- Replacing "v_tablename.table_name" with "v_tablename" on lines 15 and 18 is right.

SET SERVEROUTPUT ON;

DECLARE
  v_sql        VARCHAR2(200);
  v_tablename  VARCHAR2(50);
  tab_num      NUMBER;
  v_ref_cursor SYS_REFCURSOR;
BEGIN
  OPEN v_ref_cursor FOR
  SELECT table_name
  FROM dict
  WHERE table_name LIKE '%DBA_HIST_%'
  ORDER BY 1;

  LOOP
    FETCH v_ref_cursor INTO v_tablename;
    v_sql := 'SELECT COUNT(*) FROM ' || v_tablename;
    EXECUTE IMMEDIATE v_sql INTO tab_num;
    IF tab_num = 0 THEN
      DBMS_OUTPUT.PUT_LINE('The lines of ' || v_tablename || ' has been returned 0.');
    END IF;
    EXIT WHEN v_ref_cursor%NOTFOUND;
  END LOOP;
  
  CLOSE v_ref_cursor;
END;
/