This is a working IAM Policy for the wordpress plugin BackWPup to use with minio s3 storage.

minio-backwpup.json

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "",
            "Effect": "Allow",
            "Action": [
                "s3:ListAllMyBuckets"
            ],
            "Resource": [
                "arn:aws:s3:::*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:GetBucketLocation",
                "s3:ListBucketMultipartUploads",
                "s3:ListBucket"
            ],
            "Resource": [
                "arn:aws:s3:::<bucket>"
            ]
        },
        {
            "Sid": "",
            "Effect": "Allow",
            "Action": [
                "s3:PutObject",
                "s3:ListMultipartUploadParts",
                "s3:AbortMultipartUpload",
                "s3:GetObject"
            ],
            "Resource": [
                "arn:aws:s3:::<bucket>/*"
            ]
        }
    ]
}