Although the user has full access to S3 and the query result bucket, I’m receiving the following error while querying:

Error running query: Access Denied (Service: Amazon S3; Status Code: 403; Error Code: AccessDenied; Request ID: B0ED97AA0C5A93F1; S3 Extended Request ID: GKJvQ0s6MvOG/zO5gDtjC8EsLCOltroC/D8OAGO557N6Xfew9px3EhlDB50/BDLXb4qUko+vPI4=

Any idea?

Have you checked that your other settings are correct? The region, schema name and whatnot? Are you using IAM authentication? That error comes directly from Athena (not Redash) so you should consult their documentation as well.

Are any of the S3 buckets encrypted using KMS keys? If so the Redash user will also need kms:GenerateDataKey and kms:Decrypt permissions to the relevant KMS keys or you will get an (unhelpful!) Access Denied error.

https://docs.aws.amazon.com/athena/latest/ug/encryption.html