Although Debezium makes it easy to capture database changes and record them in Kafka, one of the more important decisions you have to make is how those change events will be serialized in Kafka. Every message in Kafka has a key and a value, and to Kafka these are opaque byte arrays. But when you set up Kafka Connect, you have to say how the Debezium event keys and values should be serialized to a binary form, and your consumers will also have to deserialize them back into a usable form.
Debezium event keys and values are both structured, so JSON is certainly a reasonable option — it’s flexible, ubiquitous, and language agnostic, but on the other hand it’s quite verbose. One alternative is Avro, which is also flexible and language agnostic, but also faster and results in smaller binary representations. Using Avro requires a bit more setup effort on your part and some additional software, but the advantages are often worth it.