First - the majority of women in the US do not use communal shower rooms, either people they aren’t members of a gym (only about 1 in 6 are), or if they are they don’t use the gym locker/shower rooms, or their gym has private changing stalls so if even if they do use the locker room they never see anyone naked nor are they themselves seen as naked.
Pretty much everyone uses the toilet, though. (In fact, toilet stalls are often used as private changing rooms)
Personal experience: In summer weather I show up at the gym in my workout clothes so no need to change. I live very close, so I choose to clean up/shower at home. (I’m also not doing mega-intense workouts). In winter I do use the locker room, but never actually strip down naked, the underwear stays on. Again, showering I do at home. I have been there when women have used the shower facilities, but have never seen anyone naked as the showers are private stalls with doors, off down a short mini-hallway. No one is standing in front of the actual lockers naked at any time that I’ve seen (although maybe it does happen). In the US women tend to avoid getting naked in public, even in a same-sex environment involving changing clothes like a locker room. I have seen women use the toilet stalls to change into workout clothes so you don’t even seen those folks in their underwear.
Second, there is this:
It’s been my experience that it’s the MEN (meaning cis men identifying as men if you want to get specific in today’s terminology) who get freaked out by trans women in the women’s locker room. I’ve long wondered if that’s some primitive fear that some strange man is going to get “their” women.
This forum had a poll of users way, way back in 2005 - here it is: Cis Women- Do you have an issue with trans women who've not had SRS in the women's room? (regrettably, the actual poll seems to have evaporate but the results are discussed in the thread) - where you see the same thing play out. By and large we cis women didn’t have an issue with it and the men were the ones most … let’s say worried.