They absolutely aren't sharing data freely with the US as is being suggested. When they are instructed to by the Swiss courts, they will share the bare minimum amount of data. This is the Swiss equivalent of being subpoenaed. It is illegal for them to share data with foreign courts unless they have received approval from the Swiss courts, who are some of the most privacy respecting in the world. You can read more here:
https://protonmail.com/blog/transparency-report/It isn't clear which data they provide.
You can read what data they have access to and can provide in their Privacy Policy:
https://protonmail.com/privacy-policy. Essentially it is your email metadata (sender, recipient, time, subject), and in some cases your IP.
