Oracle 23c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
Create Table testpo
( poid Varchar2(10),
ToDelete Varchar2(10));
BEGIN
Insert into testpo values ('PO1', 'D');
Insert into testpo values ('PO1', 'N');
Insert into testpo values ('PO2', 'D');
Insert into testpo values ('PO3', 'D');
END;
/
1 rows affected

SELECT poid,
       ToDelete
FROM   (
  SELECT poid,
         todelete,
         ROW_NUMBER() OVER (PARTITION BY poid ORDER BY ToDelete DESC) AS rn
  FROM   testpo
)
WHERE  rn = 1


POID
TODELETE


PO1
N

PO2
D

PO3
D


DELETE FROM testpo
WHERE ROWID IN (
  SELECT ROWID
  FROM   (
    SELECT ROW_NUMBER() OVER (PARTITION BY poid ORDER BY ToDelete DESC) AS rn
    FROM   testpo
  )
  WHERE  rn > 1
)
1 rows affected

SELECT * FROM testpo;


POID
TODELETE


PO1
N

PO2
D

PO3
D