Hello @Scott Roth 
I hope the target is a object reference of  HS.FHIRModel.R4.Patientand the "name" property in in R4.Patient is an object property(HS.FHIRModel.R4.SeqOfHumanName ) and thisSeqOfHumanName stores the %DynamicArray of  HS.FHIRModel.R4.HumanName object values into property called "list" 

So, First we have to check the name is  $IsObject(r4Patient.name)&&(r4Patient.name.%IsA("HS.FHIRModel.R4.SeqOfHumanName")) and if it's true you can iterate the list (%DynamicArray)   Set iter = r4Patient.name.list.%GetIterator()

You can directly copy and run this example directly and it works for me.

ClassMethod ParseHumanName()
{
    Set r4Patient = ##class(HS.FHIRModel.R4.Patient).%New()
    ;
    Set seqHuman = ##class(HS.FHIRModel.R4.SeqOfHumanName).%New()
    ; create human name for seqHuman
    Set human = ##class(HS.FHIRModel.R4.HumanName).%New()
    Set human.family="pil"
    Set human.text="Ashok,kumar"
    ;
    ;push the HumanName into SeqOfHumanName
    Do seqHuman.add(human)
    
    ; Set SeqOfHumanName into Patient.name
    Set r4Patient.name = seqHuman
    
    If $IsObject(r4Patient.name)&&(r4Patient.name.%IsA("HS.FHIRModel.R4.SeqOfHumanName")) {
        Set iter = r4Patient.name.list.%GetIterator()
        #;
        while iter.%GetNext(,.humanName) {
            zw humanName.toDao()
        }
    }
    quit
}

I have full access and permissions for the directory and %All is my role. I'm able to connect to the %SYS and USER namespaces, but I'm unable to access the namespaces mapped the HS package( c:\intersystems\irishealthcomm\mgr\hscustom\) hscustom db.

The HS.FHIRModel.R4.Patient class in  IRIS directly represents the FHIR R4 Patient resource as defined. When a FHIR Bundle is loaded using HS.FHIRModel.R4.Bundle.fromDao(), each resource in the bundle's entry.resource is automatically mapped to the correct HS.FHIRModel.R4.* subclass (e.g., Patient, Encounter, AllergyIntolerance) based on its resourceType. There’s no need for manual casting — the object model handles the typing internally.

here is the sample code

Set bundle={"resourceType":"Bundle","type":"searchset","total":3,"entry":[{"fullUrl":"https://example.org/fhir/Patient/patient-1","resource":{"resourceType":"Patient","id":"patient-1","name":[{"family":"Doe","given":["John"]}],"gender":"male","birthDate":"1985-02-15"},"search":{"mode":"match"}},{"fullUrl":"https://example.org/fhir/Encounter/encounter-1","resource":{"resourceType":"Encounter","id":"encounter-1","status":"finished","class":{"system":"http://terminology.hl7.org/CodeSystem/v3-ActCode","code":"AMB","display":"ambulatory"},"subject":{"reference":"Patient/patient-1"},"period":{"start":"2023-07-01T10:00:00Z","end":"2023-07-01T10:30:00Z"}},"search":{"mode":"include"}},{"fullUrl":"https://example.org/fhir/AllergyIntolerance/allergy-1","resource":{"resourceType":"AllergyIntolerance","id":"allergy-1","clinicalStatus":{"coding":[{"system":"http://terminology.hl7.org/CodeSystem/allergyintolerance-clinical","code":"active"}]},"verificationStatus":{"coding":[{"system":"http://terminology.hl7.org/CodeSystem/allergyintolerance-verification","code":"confirmed"}]},"type":"allergy","category":["food"],"criticality":"high","code":{"coding":[{"system":"http://snomed.info/sct","code":"227493005","display":"Cashew nuts"}],"text":"Allergy to cashews"},"patient":{"reference":"Patient/patient-1"},"reaction":[{"manifestation":[{"coding":[{"system":"http://snomed.info/sct","code":"271807003","display":"Skin rash"}]}],"severity":"moderate"}]},"search":{"mode":"include"}}]}                                                                                             
set fhirModelBundle = ##class(HS.FHIRModel.R4.Bundle).fromDao(bundle)  
;
Zwrite fhirModelBundle.entry.list.size()
3
;
Zwrite fhirModelBundle.entry.list.get(0).toDao() ; patient
{"fullUrl":"https://example.org/fhir/Patient/patient-1","resource":{"resourceType":"Patient","id":"patient-1","name":[{"family":"Doe","given":["John"]}],"gender":"male","birthDate":"1985-02-15"},"search":{"mode":"match"}}  ; <DYNAMIC OBJECT>                        
;
Zwrite fhirModelBundle.entry.list.get(1).toDao() ; encounter
{"fullUrl":"https://example.org/fhir/Encounter/encounter-1","resource":{"resourceType":"Encounter","id":"encounter-1","status":"finished","class":{"system":"http://terminology.hl7.org/CodeSystem/v3-ActCode","code":"AMB","display":"ambulatory"},"subject":{"reference":"Patient/patient-1"},"period":{"start":"2023-07-01T10:00:00Z","end":"2023-07-01T10:30:00Z"}},"search":{"mode":"include"}}  ; <DYNAMIC OBJECT>                                                                                                                         
;
Zwrite fhirModelBundle.entry.list.get(2).toDao() ; Allergy
{"fullUrl":"https://example.org/fhir/AllergyIntolerance/allergy-1","resource":{"resourceType":"AllergyIntolerance","id":"allergy-1","clinicalStatus":{"coding":[{"system":"http://terminology.hl7.org/CodeSystem/allergyintolerance-clinical","code":"active"}]},"verificationStatus":{"coding":[{"system":"http://terminology.hl7.org/CodeSystem/allergyintolerance-verification","code":"confirmed"}]},"type":"allergy","category":["food"],"criticality":"high","code":{"coding":[{"system":"http://snomed.info/sct","code":"227493005","display":"Cashew nuts"}],"text":"Allergy to cashews"},"patient":{"reference":"Patient/patient-1"},"reaction":[{"manifestation":[{"coding":[{"system":"http://snomed.info/sct","code":"271807003","display":"Skin rash"}]}],"severity":"moderate"}]},"search":{"mode":"include"}}  ; <DYNAMIC OBJECT>