Before commenting, be aware that the best one in my opinion, Drip, has been outdated for a year and something, it doesn’t even support new version of Android after 10 I think. Then Log28 has not been updated for more than 2 years and Periodical for one and a something, plus its GUI is really ugly.
So, basically there’s no option to track your period while being private now?
I found this option which looks nice and all, but it’s a really new project and it’s lacking features right now. Hope it grows to be something good, though.
F-Droid has Periodical too and it was updated 9 days back