Let you know that I have just closed the AWS account after terminating all the resources we used (I hope, at least!).
So I have temporarily reconfigured Discourse to make the backups only locally, until the new bucket in AWS is configured (by the way, @son_of_bob; if you want and have the time to configure it yourself, it would be good because then someone else would know the procedure, we could make changes later more easily, etc.).
In any case, after the new S3 service is up and running we will have to redirect the forum backups to the bucket once again, and later the staff members will have to perform the procedure for individual synchronization once again (explained in the first post of this very topic Backups, and detailed in https://discuss.actualism.online/t/personal-syncs-with-backups/138).