I use Drip for basic cycle tracking. I don’t use it for fertile phase tracking so no comment there.

For cycle tracking, it does what it needs to do. It’s easy enough to setup and completely forget what tracker/spyware I used to use. Heck, I think it was Flo I used to use.

And f-droid or another alternative app stores not mandatory, Drip is on the Google Play store at least. Not sure about Apple.