On the subject of DID... I think it's accepted that the alters are all part of the personality of the physical body
The brain uses different personality to cope with different things - protective... so an adult might need a "child" personality to seek nurturing
Or a different sex personality might have found a situation easier to cope with
But I've never heard or someone using DID to prove people are born in bodies that don't match... DID isn't something you're born with, it's a response to TRAUMA!!!! And only proves the brain copes with stress by picking out a personality who can best cope with a situation
To me that kinda proves rather than disproves the idea that forcing kids to be gender conforming might push them into thinking they are Trans