Hmmm
Here’s a thought….
I can’t speak for whether or not it’s good representation, but amnesia doesn’t usually work this way. People forget long term memories, like parents names or if they had a dog, or short term memories, like every conversation after the brain damage, but I’ve never heard of anyone forgetting general facts from anything short of dementia. People remember how to write and speak, and that the sky is blue, and they remember their gender. What you could do is have him already identify as trans and just forget about the people who didn’t support him, making it easier to transition.
What if the amnesia hits when they’re like 4 or 5 years old, and they don’t have many long term memories in the first place? What do they forget then, like surely at that young the amnesia would be like a soft reboot of the brain?