ELI5 Menstrual stages with the progestin-only contraceptive

Specifically the implant (nexplanon/implanon) since it releases etonogestrel** **and I don’t know if it’s effects differ from levonorgestrel. Entirely possible it’s the same idk. For context I have the implant, that’s why I’m wondering.

I know during a menstrual cycle, without any contraceptives, the releases/increases/decreases of hormones trigger fluctuations in other hormones which make all the physical changes happen.

How does a steady baseline of progestin change this? There must still be some hormone changes if people still get periods? Assuming there are still hormone changes during the menstrual cycle, are they largely flattened (picturing the chart of hormones over an unmedicated cycle which is very spiky and curvy)? What are the physical changes that still happen during a cycle with the contraception and why, ie what hormone is doing what?

A lot of questions so no pressure to answer them all, just trying to get a better understanding