Please don’t use AWS S3 there’s vast numbers of much cheaper compatible choices.
That being said, I plan to support more cloud platforms in the future, starting with GCP.
There are choices that speak the S3 data plane API (GetObject, ListBucket, etc).
There are no alternatives that support most of the AWS S3 functionality such as replication, event notifications.
Main problem is most support subset of the more advanced S3 features and often not all that big one. But if you just want to dump some backups in the cloud backblaze and other alternatives is cheaper