It is an open secret if you talk to any Google employee that Gmail data is heavily used to enrich other Google services, including ad placement, even if indirectly. They also can and will give it to authorities thanks to bulk keyword sharing agreements with or without individual warrants.
https://www.forbes.com/sites/thomasbrewster/2021/10/04/googl...
US citizens should take careful note of the fact their data is only usefully constitutionally protected if it is hosted at home.