The way that the full body scanner works, is someone looks at you visually first and genders you (entirely separate from gender markers on IDs). If you pass as a woman, they hit the woman button which tells the TSA agent looking at the body scans to expect things like bras but not to expect external genitals. So if a trans femme without bottom surgery goes through, she gets flagged for having a penis and another TSA agent has to make sure it’s not a concealed explosive or something, meaning said trans femme gets groped in the process. However, if the TSA agent sees a scan of a woman wearing a menstrual pad instead, that’s just a cis woman on her period, no pat-down required.

Alternatively, if someone passes as a man, they will get flagged if they are wearing a bra. So planning to navigate TSA the easiest may involve using gendered clothing to unambiguously pass as well.