If a cis girl can't lose her virginity to a tampon (and that's definitely a myth), then a trans woman can't lose it to a dilator. Plenty of cis women don't have hymens, either; some are born without one, and lots break it long, long before they lose their virginity. Of course, what's defined as "virginity" is up to the person.
(I hadn't contributed here because I count the first time my wife penetrated me, which probably isn't what most people in the thread had in mind.

My wife, btw, didn't have a hymen or bleed the first time I penetrated her...)