Right now, you’re able to select the appropriate gender marker on your passport without a note from a medical professional (and a passport can be used in the vast majority of situations you’d use a birth certificate) but because the self select gender marker was done by executive action, it’s extremely likely to be reversed when Trump takes office.
Also, having one might be a good idea in general.
I’m rushing to get my name legally changed so my updated passport can be correct. My current one has 5 more years, but so it’s all my amab info. I’m terrified of how little time is left.