DB2 select from final table update gives SQL0199 error
Looking at the Db2 for i 7.2 Knowledge Center, shows that only INSERT's are valid in data-change-table-references, not UPDATE's

https://www.ibm.com/support/knowledgecenter/en/ssw_ibm_i_72/db2/rbafztabref.htm

data-change-table-reference

|----+-FINAL-+--TABLE--(--INSERT statement--)--+--------------------+----|
     '-NEW---'                                 '-correlation-clause-'     



  If a data-change-table-reference is specified, the intermediate result table is the set of rows inserted by the INSERT statement.


The link you referenced in your original question is for DB2 for LUW (Linux, Unix and Windows) 9.7. This is essentially a different product than Db2 for i.