CapybaraSix Cross Progression was rolled out to players between October of 2023 to around April of 2024.
During this time, any platform account that was linked to the same EA Account got its Apex progress and data merged and then stored onto the connected EA Account.
If you connect a new platform account to your EA Account now, that platform account will only be able to access the Apex progress and data that was stored onto the EA Account.
That being said, if your PlayStation and Steam Accounts were linked to two different EA Accounts, and you had switched what EA Account your PlayStation Account was linked to, that sadly won't transfer, (or merge), your Apex progress and data since that was stored on the EA Account you had unlinked your PlayStation Account from, (which unlinking can also cause a loss of your Apex progress and data).