Regarding the AWS_ACCESS_KEY_ID, I allways used that. As long as I am using restic (some years) It was also always like this in the documentation. I even looked at machines where I configured restic 3 years ago and even there I used AWS_ACCESS_KEY_ID. So I am not aware if AWS_ACCESS_KEY ever worked.
Regarding the region - yeah that seems to be true. You have to use the correct region now. I did a thread about that some time ago: