Output.kafka filebeat (possible to add field ?)

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Thank you for the reply.
I have already tried these examples but didn't work i don't know where is the problem.
i tried this

processors:
  - add_host_metadata: ~
  - add_cloud_metadata: ~
  - add_fields:
      target: pathtest
      fields:
        name: '%{[log][file][path]}'

logstash.conf

mutate{
    add_field => { "[pathtest]" => "%{[pathtest]}"}
    }

it gives me
"pathtest" => "%{[pathtest]}"
and i also tried this:

processors:
  - add_host_metadata: ~
  - add_cloud_metadata: ~
  - add_fields:
      target: '@metadata'
      fields:
        op_type: "%{[log][file][path]}"

logstash.conf

mutate{
    add_field => { "[path]" => "%{[@metadata]}"}
    }

It gives me
"path" => "{\"kafka\":{\"topic\":\"kafka-topic-test\",\"consumer_group\":\"logstash\",\"partition\":0,\"offset\":72,\"key\":\"null\",\"timestamp\":1720134475223}}"
there is no op_type in metadata... i don't know if i did something wrong ?

Any help would be sincerely appreciate!
Thanks!