ORA-02097 when setting max_string_size=extended

I tried to set max_string_size=extended on my Oracle XE 18c Windows Edtn. I did it following way and got

C:\oracle\product\18.0.0\dbhomeXE\bin>sqlplus /nolog

SQL*Plus: Release 18.0.0.0.0 - Production on Fri Mar 8 18:41:10 2019

Version 18.4.0.0.0

Copyright (c) 1982, 2018, Oracle.  All rights reserved.

SQL> connect / as sysdba

Connected.

SQL> PURGE DBA_RECYCLEBIN;

DBA Recyclebin purged.

SQL> SHUTDOWN IMMEDIATE;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> STARTUP UPGRADE;

ORACLE instance started.

Total System Global Area 1610609384 bytes

Fixed Size                  9028328 bytes

Variable Size             520093696 bytes

Database Buffers         1073741824 bytes

Redo Buffers                7745536 bytes

Database mounted.

Database opened.

SQL> ALTER SYSTEM SET max_string_size=extended;