The ‘trans’ issue contributed heavily to the downfall of Nicola Sturgeon
I agree that Sturgeon's handling of issues surrounding transgender identity very much affected her, and those issues are a hot potato in the US as well, but
according to polling in the US was number 1 factor in the election of Donald Trump among ‘undecided’ voters ie Democrats who couldn’t face voting Democrat again
this is misinformation, to the best of my knowledge; I have never seen reliable polls that indicate they were the most important factor among undecided voters in the 2024 US presidential election.
Implications of transgender identity-related issues for women should not be downplayed and women should not be silenced when speaking up.
Nevertheless, some have been misconstruing those issues as the most salient one in the 2024 election, and this misinformation has seemingly spread a lot in online spaces where women's rights are primarily discussed.
The analyses I've come across showed inflation and cost of living (i.e., economy) as the most significant factors in the undecided group; could you link to an example that shows otherwise?
Yes, it's possible that some in the undecided group, such as Independent voters who were concerned about the impact the transgender movement has had on female rights, could have swung to the other side, but there has not been reliable data that demonstrated even among such voters the transgender identity issues were the most dominant vote driver.
Again, this isn't meant to silence women and erroneously claim that concerns are "nothing but fabricated", etc., because female rights are indeed impacted and women should not be ignored; this is just about the particular argument regarding the importance of those issues in the 2024 election which has yet to be completely verified.