it’s definitely derogatory in many contexts, but it is not necessarily transphobic. it has a similar history to transsexual/gender identity disorder in that it is a term originating in the medical community to medicalize and stigmatize the trans experience. transgender tends to be perceived as a term that has less baggage but that’s historically contested.
I mean to me it’s like, if people say it without knowing it’s outdated then it’s wtv, just let them know transgender is the proper term, but if they know it’s often seen as derogatory and still use it on the basis of “I’m just using proper terminology” or wtv pseudo intellectualism they want to portray them they just want a way to look down on trans people without being outright transphobic, or in addition to it.