<?xml version="1.0" encoding="utf-8"?>

xmltype(<файл> , nls_charset_id('UTF8') )

ORA-31011: XML parsing failed
ORA-19202: Error occurred in XML processing
LPX-00210: expected '<' instead of 'P'

 NLS_CHARSET_ID('CL8KOI8R') и NLS_CHARSET_ID( 'CL8MSWIN1251' ) 

declare   
   x   NUMBER;
  p_blob BLOB := empty_blob();
  p_clob CLOB := empty_blob();  
  src_loc BFILE;
  p_pathname varchar2(150):='tt.xlsx';
  tt XMLType;
begin
  src_loc := BFILENAME('INDIR', p_pathname);
   -- Open source binary file from OS
  DBMS_LOB.OPEN(src_loc, DBMS_LOB.LOB_READONLY);
  -- Create temporary LOB object
  DBMS_LOB.CREATETEMPORARY(
        lob_loc => p_blob
      , cache   => true
      , dur     => dbms_lob.session
  );
  -- Open temporary lob
  DBMS_LOB.OPEN(p_blob, DBMS_LOB.LOB_READWRITE);
  -- Load binary file into temporary LOB
  DBMS_LOB.LOADFROMFILE(
        dest_lob => p_blob
      , src_lob  => src_loc
      , amount   => DBMS_LOB.getLength(src_loc));

  --file=UTF-8, select t.value/*='CL8MSWIN1251'*/ from nls_database_parameters t where t.PARAMETER = 'NLS_CHARACTERSET'
  tt:= XMLTYPE( p_blob, nls_charset_id( 'CL8MSWIN1251' ) );  
  dbms_lob.CreateTemporary(p_clob, TRUE, dbms_lob.CALL);

  dbms_lob.convertToClob(
    dest_lob      => p_clob,
    src_blob      => p_blob,
    amount        => dbms_lob.lobmaxsize,
    dest_offset   => p_dest_offset,
    src_offset    => p_src_offset,
    blob_csid     => nls_charset_id('CL8MSWIN1251'),
    lang_context  => p_lang_context,
    warning       => p_warning
    );
    
    select dump( dbms_lob.substr( p_clob, 4000, 1 ),10) into x from dual;
    dbms_output.put_line(x);
end;       

p_clob CLOB;

DECLARE
     fil BFILE; 
     pos INTEGER;
     amt BINARY_INTEGER; 
     buf RAW(4000); 
     res VARCHAR2(250);
BEGIN 
  fil := BFILENAME('INDIR', 'tt.xlsx');
     
     dbms_lob.open(fil, dbms_lob.lob_readonly);   
      amt := 40; pos := 1; buf := ''; 
     dbms_lob.read(fil, amt, pos, buf); 
     
     select DUMP(substr(buf,1,40),1016) into res from dual;
     
     dbms_output.put_line(res);

     dbms_lob.close(fil); 
     
END; 

tt:= XMLTYPE( p_blob, nls_charset_id( 'CL8MSWIN1251' ) );

ORA-31011: XML parsing failed
ORA-19202: Error occurred in XML processing
LPX-00210: expected '<' instead of 'P'
Error at line 1
ORA-06512: at "SYS.XMLTYPE", line 283
ORA-06512: at line 25

  dbms_lob.convertToClob(
    dest_lob      => p_clob,
    src_blob      => p_blob,
    amount        => dbms_lob.lobmaxsize,
    dest_offset   => p_dest_offset,
    src_offset    => p_src_offset,
    blob_csid     => nls_charset_id('CL8MSWIN1251'),
    lang_context  => p_lang_context,
    warning       => p_warning
    );
        
    dbms_output.put_line( dbms_lob.substr( p_clob, 4000, 1 ));
end;    

select sys_context('userenv', 'LANGUAGE') from dual

select * from database_properties
where PROPERTY_NAME in ('NLS_CHARACTERSET')

DECLARE
     fil BFILE; 
     pos INTEGER;
     amt BINARY_INTEGER; 
     buf RAW(4000); 
     res VARCHAR2(250);
BEGIN 
  fil := BFILENAME('INDIR', 'tt.xlsx');
     
     dbms_lob.open(fil, dbms_lob.lob_readonly);   
      amt := 40; pos := 1; buf := ''; 
     dbms_lob.read(fil, amt, pos, buf); 
     
     select DUMP(substr(buf,1,40),1016) into res from dual;
     
     dbms_output.put_line(res);

     dbms_lob.close(fil); 
     
END;

Typ=1 Len=40 CharacterSet=CL8MSWIN1251: 35,30,34,42,30,33,30,34,31,34,30,30,30,36,30,30,30,38,30,30,30,30,30,30,32,31,30,30,36,32,45,45,39,44,36,38,35,45,30,31

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>