public sealed class RowToken 

//ArcGIS Pro 2.5 extends the EditOperation.AddAttachment method to take a RowToken as a paramter.
//This allows you to create a feature, using EditOperation.CreateEx, and add an attachment in one transaction.

var editOpAttach = new EditOperation();
editOperation1.Name = string.Format("Create point in '{0}'", CurrentTemplate.Layer.Name);

var attachRowToken = editOpAttach.Create(this.CurrentTemplate, polygon);
editOpAttach.AddAttachment(attachRowToken, @"c:\temp\image.jpg");

//Must be within a QueuedTask
if (!editOpAttach.IsEmpty)
{
  var result = editOpAttach.Execute(); //Execute and ExecuteAsync will return true if the operation was successful and false if not
}

// Create an EditOperation
EditOperation editOperation = new EditOperation();
editOperation.Name = "Create pole; create transformer bank; attach transformer bank to pole";

// Create the transformer bank
RowToken transformerBankToken = editOperation.Create(transformerBankLayer, transformerBankAttributes);

// Create a pole
RowToken poleToken = editOperation.Create(poleLayer, poleAttributes);

// Create a structural attachment association between the pole and the transformer bank
RowHandle poleHandle = new RowHandle(poleToken);
RowHandle transformerBankHandle = new RowHandle(transformerBankToken);

AssociationDescription poleAttachment = new AssociationDescription(AssociationType.Attachment, poleHandle, transformerBankHandle);

editOperation.Create(poleAttachment);

// Execute the EditOperation
editOperation.Execute();