"We disclose information such as cookie IDs, your IP address, or a hashed version of your email address to third parties, such as Facebook Ads, Google Marketing Platform, and others who may combine that information with other information they already have about you and deliver ads about Pinterest to you. We may also provide partners with information about you so that advertisers can show you ads on or off of Pinterest."
Pinterest shares user identifiers including IP addresses, cookie IDs, and hashed emails with major ad platforms like Facebook and Google, who can combine this with their own data profiles on users.