I got the same issue, too. Backup upload works but image upload shows “The bucket does not allow ACLs”
And it fixed by modifying one permission in IAM and two settings in bucket
First I changed the guide about IAM permission from “s3:HeadBucket” to “s3:ListBucket” because Amazon said HeadBucket is not a valid permission
Then I follow the guide to exactly as same as in permission page in bucket
Then the most important part, enable ACLs, it’s called Edit Object Ownership in permission tab, with ACLs enabled and set to object writer, everything just fine now
Hope my experience can help you