In GA4, with Google Signals enabled, the "identity signal" is a psuedonymous identifier unique to your Google Account. I don't know exactly if it's a hash or a

In GA4, with Google Signals enabled, the "identity signal" is a psuedonymous identifier unique to your Google Account. I don't know exactly if it's a hash or a join key or what, but the point is it's stable across devices and domains. It does not directly contain PII. Google can join it to PII, website owners cannot. It is not aggregate. You can pull the hit-level data from GA, including the identifiers being used.