Your confusing gender(social) with sex(biological) due to the common usage of male being used in both (social) and (biological) cases.

Castration is always the removal from a male because it’s talking about sex(biological) as defined by the reproductive organs the physical presence there in.

Wether or not an entity is transgender(social) or (biological) has no barring on the biological in this instance.

Bottom surgery would be the correction of physical flesh, from one reproductive organs to the other. Functional or not not withstanding.

It would be scientifically accurate to say “you castrate a male(biological) that presents female(social) in the process of correcting the biological presentation to align with the chosen social presentation”.

Such a person would be accurately termed both male and female depending on the context, being social, biological, or medical. As all three can vary depending on the person’s own choice, nature and medical history.

Medical tho depending on what field your in may be the same or different then biological. So that context gets used much less as a standalone.

But it would be impossible to castrate a female(biological) as the physical flesh that the term is in refences to physically does not exist.

Words have multiable meanings, please be careful when you are using homonyms. It can be INCREDIBLY important, and is the leading cause to almost every argument around gender.

People really REALLY need to pay attention to homonyms.

Biology is pretty much trinary. Male or female as a baseline and is mostly modified into functional/nonfunctional aspects for the purpose of reproduction. Or hermaphroditic and then again functional/nonfunctional. Biology is rather bland and sterile in terminology and doesn’t much care about anything else.

Social terminology is where the spectrum is as it’s a construct around role, view, and self presentation. Has changed various times though out history and culture.

Medical is the fun one, as depending on the field of study in question it varies insanely in terms of use. Tho it’s typically God damn important to be very exact with it cause uhh… hopefully obvious reasons.