Size mapper plugin - how to see it in Kibana?

I am going to try that again, since there where already some topics about it:

I have installed: Mapper Size Plugin | Elasticsearch Plugins and Integrations [7.15] | Elastic on my 7.13.2 cluster and I have created a new index with this mapping:

mappings": {
    "_size": {
      "enabled": true
    }
  }

I can see the _size indexed correctly in the json event:

But I cannot select this field for filtering and I cannot use this field in visualizations:

  1. How I can use the _size field now for filtering and visualization
  2. Am I able to enable the _size field in the index template?

I have set the _size in the Metafields in Advanced Settings in Kibana and now I can select this field for visualizations. Thanks to: