Dynamic Parent Child Insertion in single DML

DynamicDML.cls

// Initiaing a new list to insert
List<sObject> insertList= new List<sObject>();

//Account Object
sObject accObj = Schema.getGlobalDescribe().get('Account').newSObject();
    
// Account Object Data mapping
accObj.put('Name','Test');
accObj.put('ExtId__c','Test'); //External Id

// Adding the account to the list
insertList.add(accObj); 

//Duplicate for Lookup
//To Prevent "MORE THAN 1 External Foriegn Key provided" error
sObject accObj_clone = Schema.getGlobalDescribe().get('Account).newSObject();
accObj_clone.put('ExtId__c','Test');

//Contact Object
sObject con = Schema.getGlobalDescribe().get('Contact).newSObject();
con.put('LastName','Test Con');
// Method to dynamically add parent-child lookup (having ExternalID)
// https://salesforce.stackexchange.com/questions/161801/add-dynamic-lookup-on-contact-to-sobject-with-external-id
SObjectField accLookup = Schema.getGlobalDescribe().get('Contact').getDescribe().fields.getMap().get('AccountId'); //Getting the relationshipName
                      con.putSObject(accLookup.getDescribe().getRelationshipName(),accObj_clone); //Adding a lookup Reference
insertList.add(con);

try{
  insert inserList; // DML
} catch(Exception e){
  System.debug(e);
}