confluent-serializers-standalone.tar.gz

archive contains:

• kafka-schema-registry-package-7.0.1-standalone.jar
• kafka-serde-tools-package-7.0.1-standalone.jar

These classes allow you to use confluent serializers in debezium for confluent-compatible schema-registry. Allowed serializers: avro, json, protobuf.
Starting from version 2.0 debezium docker images not include confluent jar files - so you need to add them by yourself. But even in 1.9 debezium docker contains confluent jar files only for avro serializer.
For details see 'schema-registry-karapace-json'