The official SPARQL endpoint for DBPedia is available from https://dbpedia.org/sparql and is based on a Virtuoso engine.
It is possible to connect to this endpoint using the following configuration:
%%graph_notebook_config
{
"host": "dbpedia.org",
"port": 443,
"auth_mode": "DEFAULT",
"iam_credentials_provider_type": "ROLE",
"load_from_s3_arn": "",
"ssl": true,
"aws_region": ""
}