I have my backups working with S3 as well. So I have old and new uploads working with S3. I am using Cloudflare for SSL, DDoS, BunnyCDN for the upload and backup pull zones, and BackBlaze for the S3 storage. I’m all good now!
Note that it’s better to define the env variables in the app.yml as shown here: Using Object Storage for Uploads (S3 Clones)
Then rebuild so that the S3 configuration is globally defined and not just in admin panel. This way, when you migrate old files to s3, you can do it easier with 3 commands:
./launcher enter app
rake uploads:migrate_to_s3
rake posts:rebake