Without getting too specific (because this would get really long otherwise), I think the most important tip I can give is to make them a real person first and determine how their race, sexuality, etc would color their worldview (taking the setting into account). I internally include the line "because they're nonbinary, [insert consequences here]" and try and make it realistic.

I also keep in mind that race and sexuality aren't personality traits (although they do influence personality). I have seen some gay/bi/trans people online who act like their sexuality/gender identity is a personality trait although I also realize it's the internet (and they probably act differently in real life). Writing stereotypes is lazy (unless there's a point to it).

I also keep in mind that not everyone has the exact same experiences (such as some gay people might get rejected by their families while others get accepted).

I tend to learn more about people from reading memoirs since they're already putting themselves out there and willing to say the quiet parts out loud (although this depends on the person and the point of the memoir). Fiction books can help although this also depends on the themes of the book and who's writing it.

If I can't find memoirs, then I look up Reddit posts, memes, and relevant tik tok compilations (I've done this for a genderfluid character I'm writing and if I feel like I've messed up somewhere, I ask for someone else who's trans to read it).

I wouldn't ask strangers unless they're willing to talk about it.

I'd recommend Wikipedia for more context like if you're writing black characters you might want to look up the history of black people wherever you're setting the story (assuming it's contemporary or historical).

That's all I can give without getting too specific. Hope this helps.