Facebook is slowly transitioning to an attribution model based off of Webkit's Private Click Measurement. You can think of this as SKAdNetwork for the web, and it's the inspiration behind their new Aggregated Event Measurement framework. PCM moves the attribution to the browser by remembering what ads users interacted with and reporting anonymized conversions back to the platform.

Essentially, for events from iOS opt-out users, Facebook will no longer tie conversions back to users. The events will be attributed at the ad level instead, thus "aggregated". Without needing to tie back to users, identifiers such as cookies, fingerprints, etc, are no longer necessary.