From https://developer.mongodb.com/community/forums/t/kafka-source-connector-kafka-schema-registry-and-ksql-schemas-inconsistencies/8287/2

The configuration option output.schema.value is very important, but its usability can be frustrating. In our case, we work with complex schemas and having to write them down as a string is very error prone and difficult to debug for these same errors that may happen.
My suggestion would be to allow the specification of a schema by giving the path to a schema file. The supported types I would also suggest would be at least .json and .avsc files.