Big big risk here having spent last 6 years working for the largest provider of adult live porn cams, FOSS isn’t the issue but regulation and safety and infrastructure to ensure everyone participating is a consenting adult and not being trafficked or abused is a huge problem around the world. I may incur downvotes for this opinion, but this is a space where it SHOULD be regulated with a lot of checks and balances. You don’t want to accidentally come across CSAM and have that cached in your temp files for so many reasons.

Bodies don’t have a set schedule for things. An AFAB body is supposed to routinely ovulate and have a period, but lots of things can disrupt that and cause things to happen early or not at all or delayed. Tracking becomes important for a lot of medical reasons, but a common situation in which it’s important to track is for conceiving. And yes privacy is a huge risk with using an app to track, and with how the government in the US is currently talking about punishing women for not conceiving or having miscarriages etc