Quick, someone define the difference between a nonbinary transmasc he/him lesbian or bi-lesbian and a heterosexual or bisexual nb transgender man, beyond the label chosen to describe one's experience, without relying on gender essentialism!
"One of them is a lesbian and one of them is a man!"
What's in a word? What defines someone as a nb he/him ftm lesbian and someone as a nb trans man?
"A lesbian is a woman who loves women"
The nb transmasc lesbian is not a woman and he doesn't wont you to call him or his girlboyfirend one.
Beyond a label chosen for whatever personal reasons someone has to describe there gender and sexuality, you can not put these two (or any other queer identity) in a box with no overlap.
I'm a man becouse it feels good for me to be one and it makes me happy, but up until the point where I defined myself a man, my experience could have been easily considered that of a nb transmasc lesbian. The reason I'm not is becouse I realized being a man felt better and than I realized by becoming one that I love men very dearly and that they are important to me. Outside of the word I use and that I no longer focus my sexuality on women, there is very little difference.
As a trans man I now have experiences that are very specific to transgender men, but prior to this, I was a lesbian and that's something that I don't care to pretend wasn't there, I just found that I was less and less happy as one and at some point I realized that being a man made me happy the way being a lesbian had as a younger teenager and than it made me even happier and kinder and healthier.
Gender and sexuality are a scam and the only way to come out with the least amount of bruises and loss, is to throw away petty labels and language that will never be able to define a person and just use whatever makes you feel good whenever you want and however you want, there are no rules that do not aim to hurt you.