Body doesn’t equal gender so you may indeed be agender and find yourself more comfortable in a body with estrogen vs testosterone. Sex drive, desires about sex can change on HRT but there isn’t research pointing at any particular cause. Mostly there’s a noted correlation but that does not imply causation. There’s a number of confounding factors that would make determining that definitively difficult. Dysphoria masking is a thing and it could be involved but that’s not necessarily what’s happening. There’s certainly a possibility that you are adopting someone else’s opinion of what your body should be.
My advice would to spend more time thinking about how you want to be, and what you might want to do about that. The best solution to figuring out what you want is to think about how you perceive things now, and consider if that’s good and enjoyable for you or if it’s not. And also to think about if changing something would make your experience better or meet a need you have.
While I can’t say for certain, the past 10 years apparently evaporating could be a sign of some level of disassociation. Definitely something to ask your therapist about.