I got you going again mostly by following Move a Discourse site to another VPS with rsync.
Your move was complicated a bit more by your having backups on S3 configured in the database rather than in ENV variables as described in Configure an S3 compatible object storage provider for uploads (though that is for uploads, so you’d need to not use the use_s3 setting, just the backup bucket and location. EDIT: And then the restore failed because your EC2 doesn’t have write access to the bucket.
Having a load balancer in front of your site also changes things from how things are for most people.
And since your credentials are for the EC2 rather than having them in the database or the YML file, the restore can’t complete.