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.
This reminds me: In countries like Russia and China, it's not unusual for police to just randomly stop people and search their phones, at which point even locally stored data isn't safe anymore. This could happen in America as well.