There are two blank lines(9,10) which can be dropped.

1 <match **>
2 @type kafka2
3 brokers my-cluster-kafka-bootstrap.amq-aosqe.svc:9093
4 default_topic topic-logging-app
5 use_event_time true
6 username "#

{File.exists?('/var/run/ocp-collector/secrets/kafka-fluent/username') ? open('/var/run/ocp-collector/secrets/kafka-fluent/username','r') do |f|f.read end : ''}

"
8 password "#

{File.exists?('/var/run/ocp-collector/secrets/kafka-fluent/password') ? open('/var/run/ocp-collector/secrets/kafka-fluent/password','r') do |f|f.read end : ''}

"
9
10
11 ssl_ca_cert '/var/run/ocp-collector/secrets/kafka-fluent/ca-bundle.crt'
12 ssl_client_cert "#

{File.exist?('/var/run/ocp-collector/secrets/kafka-fluent/tls.crt') ? '/var/run/ocp-collector/secrets/kafka-fluent/tls.crt' : nil}

"
13 ssl_client_cert_key "#

{File.exist?('/var/run/ocp-collector/secrets/kafka-fluent/tls.key') ? '/var/run/ocp-collector/secrets/kafka-fluent/tls.key' : nil}

"
.....
</match>