There's all kinds of nonbinary identities, the term is more like a catch-all category and not at all like a distinct "third gender." And how to approach physical changes varies as much among nonbinary people as our understanding of gender. There's nonbinary people who differ from cis people mostly in how they view themselves and gender and who do not transition at all. There's nonbinary transfems like me who go by she / her exclusively, present feminine, who can best describe themselves as women to the average cis person and who require the full range of medical procedures that you'd classically think of when picturing your average trans woman, yet our relation to our gender is actually a deeply nonbinary one that's closest to the understanding of these lesbians who view "lesbian" not as a sexuality, but a gender indentity. I even know an afab person who is nonbinary / agender, goes by gender neutral pronouns, has a very androgynous style (think butch lesbian, but with cutting edge makeup and hairstyling skills) yet dey underwent the full range of laser hair removal because in spite of being afab, dey used to sport more facial hair than your average cis guy and where very much not happy with that. Then there's forms of bottom surgery whose entire point it is to create ambiguous genitals, like penile-preserving vaginoplasty, or phalloplasty without a vaginectomy, and these are mostly (but not exclusively) requested by nonbinary people. I know enbie transmasc people who adjust their low dose testosterone regimen to just masculinize themselves in specific ways (like lowering their voice, but not getting bottom growth), a ton of transmasc enbies undergo mastectomies, there's transfem enbies who only go on estradiole until they've grown boobs and then stop and go back to living on testosterone. There's all kinds of possibilities for gender affirming care, i honestly think we've only just begun to see what's possible because nonbinary people were gatekept from transitioning for such a long time.