I suggest reconsidering the use of https://hl7.eu/fhir/laboratory/StructureDefinition-Patient-eu-lab.html instead of the extension for patient.sex, which is really what lab reference ranges oare based on - see https://hl7.org/fhir/us/core/StructureDefinition-us-core-patient.html for choices around this topic.

The Gender Harmony IG (https://hl7.org/xprod/ig/uv/gender-harmony/) has described the desired characteristic as "Sex Parameter for Clinical Use" (https://hl7.org/fhir/extensions/StructureDefinition-patient-sexParameterForClinicalUse.html - and more detail is here: https://hl7.org/xprod/ig/uv/gender-harmony/design.html) and that is not used at the patient level, so if you are following that instead, then leaving patient.gender here to capture the gender identity may work.