ElasticSearch 8 errors with Action/metadata line [1] contains an unknown parameter [_type] status:400

Question

I am trying to setup EFK (ElasticSearch 8, FluentD and Kibana) stack on K8S cluster (on-premises)

I followed this link to install elasticsearch and installed it using helm charts and followed this link to install fluentd

Output of fluentd and elasticsearch pods

[root@ctrl01 ~]#  kubectl get pods
NAME                                                     READY   STATUS    RESTARTS   AGE
elasticsearch-master-0                                   1/1     Running   0          136m

[root@ctrl01 ~]#  kubectl get pods -n kube-system
NAME                                                            READY   STATUS    RESTARTS   AGE
fluentd-cnb7p                                                   1/1     Running   0          107m
fluentd-dbxjk                                                   1/1     Running   0          107m

However, elasticsearch log was piled up with the following warning messages

2021-10-18 12:13:12 +0000 [warn]: temporarily failed to flush the buffer. next_retry=2021-10-18 12:13:42 +0000 error_class="Elasticsearch::Transport::Transport::Errors::BadRequest" error="[400] {\"error\":{\"root_cause\":[{\"type\":\"illegal_argument_exception\",\"reason\":\"Action/metadata line [1] contains an unknown parameter [_type]\"}],\"type\":\"illegal_argument_exception\",\"reason\":\"Action/metadata line [1] contains an unknown parameter [_type]\"},\"status\":400}" plugin_id="out_es"
2021-10-18 12:13:12 +0000 [warn]: suppressed same stacktrace

Conf file (tailored output)

2021-10-18 12:09:10 +0000 [info]: using configuration file: <ROOT>
  <match fluent.**>
    @type null
  </match>
  <source>
    @type tail
    @id in_tail_container_logs
    path /var/log/containers/*.log
    pos_file /var/log/fluentd-containers.log.pos
    tag kubernetes.*
    read_from_head true
    format json
    time_format %Y-%m-%dT%H:%M:%S.%NZ
  </source>
  <source>
    @type tail
    @id in_tail_minion
    path /var/log/salt/minion
    pos_file /var/log/fluentd-salt.pos
    tag salt
    format /^(?<time>[^ ]* [^ ,]*)[^\[]*\[[^\]]*\]\[(?<severity>[^ \]]*) *\] (?<message>.*)$/
    time_format %Y-%m-%d %H:%M:%S
  </source>

I am not sure which 'type' field it refers to. I am unable to find an example of ElasticSearch 8 for match and source directives to compare

It seems type field is not supported from ES 8 onwards but I am not sure on that. Kindly let me know the reason for the error