Amazon S3 introduces a new S3 Object Ownership setting, Bucket owner enforced, that disables access control lists (ACLs), simplifying access management for data stored in S3. When you apply this bucket-level setting, every object in an S3 bucket is owned by the bucket owner, and ACLs are no longer used to grant permissions. As a result, access to your data is based on policies, including AWS Identity and Access Management (IAM) policies applied to IAM identities, session policies, Amazon S3 bucket and access point policies, and Virtual Private Cloud (VPC) endpoint policies. This setting applies to both new and existing objects in a bucket, and you can control access to this setting using IAM policies. With the new S3 Object Ownership setting, you can easily review, manage, and modify access to your shared data sets in Amazon S3 using only policies.
Source:: Amazon AWS