Crowd anonymity refers to the level of data you get from SKAdNetwork 4 and is based on the number of installs from the marketing campaign. It’s Apple’s new term for privacy thresholds in SKAdNetwork version 3.
On a high level, crowd anonymity is easy to understand: as the number of app installs per ad campaign goes up, so too does the level of crowd anonymity. As crowd anonymity goes up, Apple will enable more data capture for measuring campaigns, meaning that advertisers can get more data about campaign performance and can improve their ad strategies quicker.
It’s important to note, however, that no amount of extra data will reveal people’s personal data: all data is aggregated and anonymized.