@alice I've always considered them separate...

Transgender seems like more of a journey, often involving meds and sometimes surgery, in the goal of making one's sex match one's gender.

Non-binary, otoh, usually eschews all of that and completely ignores sex for a blended gender.

There are definitely similarities, and what I described above is far from clear-cut lines, but there are enough differences to necessitate a second category, imo.