Invalid resource attribute MytargetGroup for resource Outputs

I'm looking to get arn output of the target group. What is the correct way? I've tried the following and nothing works so far.

  ### Target group ###

  MyTargetGroup:
    Type: 'AWS::ElasticLoadBalancingV2::TargetGroup'
    Properties:
      HealthCheckEnabled: true
      HealthCheckIntervalSeconds: 30
      HealthCheckPath: /
      HealthCheckProtocol: HTTP
      HealthCheckTimeoutSeconds: 5
      HealthyThresholdCount: 5
      Matcher:
        HttpCode: "200,302"
      Name: target-group-1
      Protocol: HTTP
      Port: 80
      UnhealthyThresholdCount: 2
      VpcId: !ImportValue vpc-id

  #### Outputs ####
  
  Outputs:
    MyTargetGroupOutput:
      Value: !GetAtt MyTargetGroup.TargetGroupArn

Errors

cfn-lint

[cfn-lint] E3001: Invalid resource attribute MyTargetGroupOutput for resource Outputs

Cloudformation

An API call to CloudFormation.UpdateStackSet (RequestId: f1581762-6a59-41eb-802e-9927f849a7be) returned a ValidationError error: Invalid template resource property 'MyTargetGroupOutput' (Service: AmazonCloudFormation; Status Code: 400; Error Code: ValidationError; Request ID: bf04faf2-9dee-4874-9069-7a41a5b4d503; Proxy: null)

According to this document, it should work as I have above, but it doesn't.

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-elasticloadbalancingv2-targetgroup.html