You can configure the serializer here project > config > packages > framework.yaml to get conversion from camel case to snake case.

# see https://symfony.com/doc/current/reference/configuration/framework.html
framework:
    # ... omitted ...

    serializer:
        name_converter: 'serializer.name_converter.camel_case_to_snake_case'

    # ... ommitted ...

ℹ Source: https://symfony.com/doc/current/reference/configuration/framework.html#name-converter