There was a case in Canada a few years ago of a man changing his legal identity to be female in order to get cheaper car insurance. That discrimination is still legal in Canada, or was then, at any rate. As several PPs have said, it's not been legal here for years.
Really hard to see what other advantages they might gain from being female other than the usual: access to female-only spaces, which they might want for sexual reasons; getting places on female-only lists, such as "woman of the year", or filling the female quota on boards, which presumably only affects a minority; being thought "stunning and brave".
In other countries it might be a handy way of getting out of conscription. There was an interesting story a while ago about what was happening in Spain, with male soldiers changing legal sex to get some of the benefits accessible only to female soldiers:
https://nypost.com/2024/03/06/world-news/spanish-soldiers-changing-gender-to-female-for-added-benefits/