In order to deactivate cross save and unlink an account - you will need to have the login. You will need to work with PS support to regain access, and if you cant then your setup cannot be altered and the account can't be unlinked. Bungie will not step in and forcibly remove an account nor will they deactivate cross-save for you so you can move to another profile. [quote]I forgot the login to one of my accounts linked for Cross Save. Destiny Player Support and Bungie cannot modify or remove accounts linked to Bungie.net profiles. To protect player privacy and data, you must be able to log in to any linked accounts to prove ownership prior to modifying your linked account. If you no longer have access to a linked account, you will need to reach out to the specific platform’s support for assistance with account recovery options.[/quote] https://help.bungie.net/hc/en-us/articles/360049498031-Destiny-2-Cross-Save-Guide

To add what viiTactiiCZz said, it appears as though Cross Save was set up with PSN as the active account, so deactivating the feature would cause you to lose access to those characters on other platforms.