I can't help much in the POC department. I am mixed, but I appear white and I really don't know much about my culture (rip). However, I am an mlm transguy, so I'll give my two cents there.

There are simply no trans characters that aren't comedy relief. I can name like 2, and they all look like they poorly pass despite being adults. Most trans people who are adults and a few years into their transition can pass with flying colors. It's also not like...the center of our personality? Sure, I'm trans, I might put a pride flag on my bag if I'm feeling cool, but it's not something we flaunt around (for me it's out of the fear of getting a hate crime against me lmao). The other thing is that our personality isn't 100% depressed. Yes, I have depression, my trans partner does too, but we're not happy-sucking vampires. 

Also, the trope that all nonbinary characters are nonhuman or "????? gender" mysterious children. Nonbinary people are people, not aliens. Sure, it's cool if your fictional alien culture has different genders, but there are more than two genders on Earth as well...haha. Nonbinary also doesn't mean androgyny. Many enby people like being androg, but some don't. My best advice? Just talk to trans people. Making this thread was a good step in that direction. 

ALSO, I have no idea if you wanted to include mental illness and neurodivergency in this thread, but I'd be happy to talk about it.

EDIT: Basically, just like any character you're writing, avoid outdated cliches lol