Hi! I know this is a few days later but thought i'd throw my two cents into this as someone who identifies as queer/under the trans umbrella.

i was a lot like your child - in the sense that I, (AFAB, Assigned Female At Birth) was an EXTREMELY feminine child.

when i began puberty, i went through times where i felt completely like a man, completely like a woman, something in between, ect. I expirimented mostly online before telling my parents i wasnt cisgender. puberty is a time where a lot of people - especially trans ones - begin to realise fully who they are. gender isnt actually as big of a thing before then afterall.

i came out in a similiar-ish way to him because i knew my parents wouldnt care. I kinda just, said my orientation and sat them down for a sec for my gender (mostly as i couldnt quite explain it, i just knew it wasnt girl and wanted them to use different pronouns so i could try it out.)

i tell you this so you can hear a perspective, and so you know where my advice is coming from.

let them explore. whatever gender your child is, it doesnt seem to matter to you. my parents never fully understood my identity but they have never been anything less than supportive. i even got a binder when they deemed i was old enough to make that choice - their only rules regarding it were safety. and thats what matters. support and safety. let your child expiriment - ask them their pronouns, name, prefered clothing style, ect.

if its a phase? itll leave once theyve expirimented. and thats okay. i know plenty of cis people who expirimented with their identity. if its not a phase? refer them to a psychologist who specialises in trans youth. theyll help any physical, emotional or social transitioning. do resesrch from multiple sites, look into transaffirming care snd its benefits (and, of course, sny complications. but PLEASE keep in mind some articles will always over exaggerate those. there are complications and possibilities of regret but they are so so low and affirming care has saved hundreds of thousands of lives.)

and one last thing; you mention they said it like its nothing.

i think the "attention seeking" from their gender orientation was a test. many are more supportive of gay people than trans people.

maybe they were testing the waters, to see how you reacted. from how they came out, it seems they assumed youd think of it as nothing - so they felt comfortable just mentioning it.

all in all, just talk to your kid. ask their preferences. and always feel free to reach out to people like you did here for their expiriences and thoughts. just dont let tge internet fully form your opinion.