If someone woke up tomorrow and said "I have a deep, personal sense of identity that I am left handed even though I write, pitch, draw, shoot, and open doors with my right hand" nobody would take them seriously. "Identity" as I keep saying is not just a way to make something you want to be into something you are (or are a special kind of "are")
If someone woke up tomorrow and said "I have a deep, personal sense of identity that I am left handed even though I write, pitch, draw, shoot, and open doors with my right hand" and then proceeded to cut their right arm off in order to force themselves to be left handed they'd be sanctioned under the Mental Care Act.
We keep getting told "Sex is different because I say so" but it never goes any further than that. We never get told why beyond just further and more emphatic "because we say so."
"Identity" is not THIS sacrosanct no matter how many adjectives you put in front of it. "It's a deeply personal deeply help personal deeply personal internal personal deeply deep deepity deep held personal belief."
"I want to be left handed" makes perfect sense.
"I want to be left handed therefore I can declare myself either fully left handed or some special adjacent kind of left handed without changed which hand I actually use" is gibberish.
"I present as a left handed person in every way that isn't which hand I use" is gibberish.
"I live the life of a left handed person in every way that isn't which hadnd I use" is gibberish.
The entire concept of the "Self Identify" subtype of Transgender is saying exactly that. "I identify as a man in everyway except having a penis." We keep told told that is some special and different thing but never why.