S3 bucket policy to enforce encryption and https:// access

s3BucketPolicyEncryptionSSL.json

{
	"Version": "2008-10-17",
	"Id": "Policy-GENERATED-ID",
	"Statement": [
		{
			"Sid": "DenyUnSecureCommunications",
			"Effect": "Deny",
			"Principal": {
				"AWS": "*"
			},
			"Action": "s3:*",
			"Resource": "arn:aws:s3:::S3-BUCKET-ID",
			"Condition": {
				"Bool": {
					"aws:SecureTransport": false
				}
			}
		},
		{
			"Sid": "DenyUnEncryptedObjectUploads",
			"Effect": "Deny",
			"Principal": {
				"AWS": "*"
			},
			"Action": "s3:PutObject",
			"Resource": "arn:aws:s3:::S3-BUCKET-ID/*",
			"Condition": {
				"StringNotEquals": {
					"s3:x-amz-server-side-encryption": "AES256"
				}
			}
		}
	]
}

Your DenyUnEncryptedObjectUploads condition only deny aws:kms and still allow no encryption at all

"Condition": {
  "StringNotEquals": {
    "s3:x-amz-server-side-encryption": "AES256"
  }
}

To disable no encryption (but sill allow both aws:kms and AES256 you should do

"Condition": {
  "Null": {
    "s3:x-amz-server-side-encryption": "true"
  }
}

see https://aws.amazon.com/blogs/security/how-to-prevent-uploads-of-unencrypted-objects-to-amazon-s3/