> Why does a period tracking app need to send data to meta (why does it even need networking access at all)?

In case you want to sync between multiple devices, networking is the least hassle way.

> Why is there no affordance of user-level choice/control that allows users to explicitly see the exact packets of data being sent off device? It would be trival for apps to have to present a list of allowed IPs/hostnames, and users to consent/not otherwise the app is not allowed on the play store.

I don't know that it ends up being useful, because wherever the data is sent to can also send the data further on.