@visch try replacing from_dict with this:

def from_dict(cls, data, definitions=None, **schema_defaults):
        '''Initialize a Schema object based on the JSON Schema structure.

        :param schema_defaults: The default values to the Schema
        constructor.'''
        kwargs = schema_defaults.copy()
        properties = data.get('properties')
        items = data.get('items')
        defs = data.get('definitions') if definitions == None else definitions

        if properties is not None:
            kwargs['properties'] = {
                k: Schema.from_dict(v, definitions=defs, **schema_defaults)
                for k, v in properties.items()
            }
        if items is not None:
            kwargs['items'] = Schema.from_dict(items, definitions=defs, **schema_defaults)
        for key in STANDARD_KEYS:
            if key in data:
                kwargs[key] = data[key]
        if data.get("$ref", "").startswith("#definitions/"):
            kwargs.update(defs[data["$ref"].removeprefix("#definitions/")])
        return Schema(**kwargs)

Seems to work for me to make refs work, although I have not tested it recursively; not sure if JSON schema allows recursive or not.