FYI there are some apps on the F-Droid store that probably won't have to protect any data from the authorities because it stays in your phone and is not sent anywhere to begin with.
Or they could just store the data locally on the user's device and not transmit it back to a central server, such that the company never even has possession of the data nor any way to retrieve it? Like I get it would require a major rewrite if they weren't already doing this, but at least they'd be keeping their users safe while also having no way for authorities to gain any data.
Fwiw, this article says the name of the app is Clue. As a dude, I have no need of such an app, but as a security minded individual, will encourage my female friends to use it if needed and hope the developers continue to have security in mind.
Virginia Governor Glenn Youngkin has blocked a bill in the state that would have banned law enforcement from enforcing search warrants for menstrual data stored in tracking apps on mobile phones or other electronic devices,
And as a Virginian, I will once again vote against the enemy of security and privacy: Glenn Youngkin.