They don’t have any kind of hormone syndrome that mimics PMS because that’s caused by a drop in progesterone which triggers prostaglandins to rise in the uterine muscle (and also a bit in the muscles of the surrounding bowel tissue).
Oestrogen is at its lowest at this point, but it’s actually fluctuations in progesterone that triggers PMS. Prostaglandins are responsible for pain, bloating and cramps. Progesterone inhibits prostaglandin production. Period symptoms, including cramps and bloating, digestive upset, etc. are triggered when progesterone rises then drops sharply at the end of the cycle (which in turn is triggered by the corpus luteum, the body left behind after the egg is released). This drop in progesterone allows more prostaglandins to be produced in muscle.
This is GCSE-level biology, yet still we get the nonsense claim that trans women (on a consistent dose of oestrogen throughout the month) are experiencing a menstrual “cycle”. Even if they are among the vanishingly small number of trans women taking any kind of progesterone, it’s the absence of oestrogen and progesterone that causes PMS and cramps!
It all makes zero sense, and, I can confidently say, is made up nonsense that is part of playacting “being a woman” (or, to be a little charitable, possibly psychosomatic in a few people who really fervently want to believe in it). Either way, it’s disappointing that this fact-free scientifically illiterate nonsense has been allowed to take hold, and is being propagated by companies selling products to actual women and girls.