When you optimize the property inside the Pagelist, the Declare index would be automatically created. Could you please check the records of Declare Index and Class if a new one got created.

Are you trying to optimise the property which is inside the pagelist?

You can also create it manually: https://community.pega.com/sites/default/files/help_v83/procomhelpmain.htm#rule-/rule-declare-/rule-declare-index/main.htm

Declare index will be created only if you optimize property available in page list/group properties.

OOTB wizard will create an index class, new DB table, Declare index. Keys for the class will be generated automatically, it is not advised to create all of these rules manually as you need to take extra care of keys and all as you can leverage OOTB wizard for the same.