Oracle SYS users cannot set read only at session level

Official documentation reference:

SYSDBA is used internally in the Oracle database and has specialized functions. Its behavior is not the same as for generalized users. For example, the SYS user cannot do a transaction level consistent read (read-only transaction). Queries by SYS will return changes made during the transaction even if SYS has set the transaction to be READ ONLY. Therefore export parameters like CONSISTENT, OBJECT_CONSISTENT, FLASHBACK_SCN, and FLASHBACK_TIME cannot be used.

When conducting Oracle transaction-related experiments, try to use ordinary users, because many transaction-level settings can not get the correct results for sqlplus / as sysdba connection mode.

If you want to give the user access to a data dictionary for the purpose of the experiment, you can give the user the following permissions:

GRANT CONNECT,RESOURCE,SELECT ANY DICTIONARY,SELECT ANY TABLE TO TUSER

Reference: How To Connect As SYSDBA When Using Export Or Import (documentation ID 277237.1)