It's a mental health condition.

I actually think there's about 4 or so different ones that are under this umbrella but are all viewed the same in public discourse.

MTF have historically been the most common so understand more from them.

1. Early onset gender disphoria. Kids show disphoria from very early age, acts more like a girl, gets very upset when not allowed to wear female clothing, typically goes along with some kind of weird hormonal issues. Kid is likely to transition later in life, or just be gay. This is historically the most accepted version though it's quite rare. You'll probably never notice these people are they don't usually want to be in the public eye and otherwise act normal.

2. Middle age onset. This is when you get guys who are already married or whatever suddenly deciding they are women and transitioning and dragging their SO along for the ride. This is probably a kind of narcissism. These people are usually really annoying and kinda rapey in a lot of circumstances. These are the kind of people that get off going into women's spaces and exposing themselves. Not sure if it's a true mental condition or simply some kind of fetish. Pretty sure most are autogynophiles.

FTM are a bit different. I think most now are a social contagion, I think a lot of it has to do with body acceptance issues. But I know far lass about these.

I've only known a couple of trans people not very well, knew one guy that transitioned in college and went from being kinda a shy artsy pansexual type kid to a sex obsessed voyere. So that person burned through their contacts outside the LGBTQ+ bubble quite fast. New someone else who did it just for attention basically and would constantly go off on people who would comment or stare, backfired hilariously because everyone ended up just avoiding them completely leaving less attention.

I think that our society would be far better off if we payed less attention to them. I've never been convinced that surgical or hormonal treatments are the proper way to go about treating disphoria, but disphoria itself is certainly a real issue that people deal with and I can be sympathetic of that. But I don't think the disphoria is the root cause of their issues, rather it's a symptom of them not accepting themselves. So if at your core you don't accept yourself and don't feel confident, you might go try to find some external reason for why that is, but if you focus on your gender being that reason, and then you change it, there's a high risk that you'll still feel the same way after, since disphoria is essentially you feeling out of place with yourself, and even if you change your body, you're still you, and you still won't accept you.