Is it permissible for a woman to publicly discuss menstruation, or saying that she is on periods, such as on social media posts? Some call it immodest, others argue for transparency, so what is the right approach?
It is permissible to discuss menstruation.
Attitudes towards menstruation are largely cultural. What is the right approach depends on circumstances. In general, with social media, regardless of the topic, it is good to discuss things for a good reason (so, for instance, in this case, trying to break cultural stigmas and taboos about menstruation). It is not good to discuss things for the wrong reason (for instance, trying to gain attention or monetization through discussing menstruation by coming across as edgy or rebellious). Frequently, with social media, people have mixed intentions. Part of wisdom in life is sensing when it is good to respect social expectations and when it is good to break them.