I use proper date format for both employeeHireDate time and employeeLeaveDateTime which is “YYYY-MM-DDThh:mm:ssZ” as per https://learn.microsoft.com/en-us/entra/id-governance/how-to-lifecycle-workflow-sync-attributes

Provisioning log states that both attributes in Azure have been updated Provisioning Log, but when checking in Graph Explorer/MgGraph, employeeHireDate has value, but employeeLeaveDateTime is null Graph Explorer Output

Both attributes are synced with Direct mapping rule.

Custom schema attributes:

                "urn:ietf:params:scim:schemas:extension:itixcustom:1.0:User": {
                    "employeeType": "internal",
                    "HireDateTime": "2024-07-07T01:00:00Z",
                    "LeaveDateTime": "2033-07-07T21:00:00Z"    
                }

Direct mapping:
Direct Mapping

API permissions assigned to Service Principal which is calling /bulkupload API:
API Permissions

As a workaround I can do a separate call to GRAPH API to update employeeLeaveDateTime – you need
following Graph API for this: User-LifeCycleInfo.ReadWrite.All – Allows the app to read and write the lifecycle information like employeeLeaveDateTime of users in your organization, without a signed-in user. But it doesn’t really meet the expectations of /bulkupload