First and foremost, people are people. Some identify more with cultures related to their identities than others, who may be similar to them in terms of what "categories" they could fit into.

Gay people exist. Trans people exist. The LGBTQ+ exist. It isn't special to have queer characters in your writing. Unless your characters are facing some sort of ongoing battle against their sexual/gender identity, their gender and sex is unlikely to be a main focus for them.  AKA, a person who builds their personality around a single or a couple identities tends to come off as superficial and likely won't be a fan favorite or even relatable. 

Aside from works of satire, a person's identities are just a natural part of who they are. They will not be forced - if written well. Like black hair or five fingers, a person may be born with dark skin, or a clubbed foot. When people are born a certain way, they feel it is normal - because it is for them. Chances are, unless something is occurring within the story (or has occurred) that emphasizes one of these born traits, said trait(s) won't be on the forefront of the character's mind.

Not all people with mental illnesses are aware that they have a mental illness, or they may know something is off but not what exactly is wrong. Not everyone has a diagnoses.

Do research if you plan on writing about a culture that exists already. Especially look into individual testimonials of people from that culture, and from those who practice it. Educate yourself. Also, finding yourself a sensitivity reader doesn't hurt.

Intellectual diversity is integral to writing an interesting story. Don't vilify characters that YOU disagree with in real life - treat everyone like the humans that they are, even the villains. The more we readers see ourselves in uboth good guys and bad guys, the more compelling the story is to read. And it tends to be obvious to readers when a certain character is a caricature, rather than a person. If the intention is to make a caricature, that's one thing, but keep in mind doing so may lead to certain unpleasant responses from readers. 

Be sure to distinguish each character - as well as yourself from the narrator(s).