Conscription for trans folk in the US is also fucked up. Trans women, regardless of their gender identity being legally recognized or not, still have to sign up when they are 18. Trans men are not legally required to, despite anyone’s opinion on whether they should if they come out and transition before the age of 26. Should any FtM or other sibling, born AFAB, who usually checks off “male” on forms that do not register a non-binary option want to apply for college or certain governmental jobs but don’t want to conscript, there is an alternative—the SIL, or “Status Information Letter”. You can present the letter and not out yourself, or the very least constantly have to upload or mail out forms showing you have transitioned—it’s just one letter, and you’re covered.
Getting it takes time (usually about a month or so, longer with COVID). All you need is a letter from your doctor stating you’re receiving “proper treatment” (no, you don’t need to detail if and what you’re doing, especially if aren’t doing anything to transition), and you should be good. Just mail a copy (not originals, they won’t mail anything back) of your birth certificate, photo ID, SS card, a letter from your doctor, any legal documentation if you changed your name and your documents aren’t all in the same name, and the form stating why you seek a SIL.
They will only mail one copy. I recommend you scan a copy to keep digitally available, and keep the original locked away with your other valuable documents.