const app1= new cdk.App();
const stack1 = new cdk.Stack(app, "stack1");
const stack2 = new cdk.Stack(app, "stack2");

const topic = new Topic(stack2, 'Topic');

const bucket = new s3.Bucket(stack1, "bucket");
bucket.addEventNotification(      EventType.OBJECT_CREATED_PUT, new s3n.SnsDestination(topic));

$ cdk synth

Error: 'stack1' depends on 'stack2' ("stack1/bucket/Notifications/Resource" depends on "stack2/Topic/Resource", "stack1/bucket/Notifications/Resource" depends on "stack2/Topic/Policy/Resource", stack1 -> stack2/Topic/Resource.Ref). Adding this dependency (stack2 -> stack1/bucket/Resource.Arn) would create a cyclic reference.