setting up an autochange in the cloud

Trying to set up an autochanger using a S3-compatible bucket in "the 
cloud" (in my case at Contabo in germany).

Fresh installation of Bacula-15.0.2, Bacularis-4.0.0 on a Debian-12.7 
machine.

Added the packages:  bacula-cloud-storage-s3 plus 
bacula-cloud-storage-common

Restarted all the daemons.

Looked at https://www.youtube.com/watch?v=MRdM2uKlHSI ... I don't get 
that "Add cloud storage" button to begin with ...

Trying to edit bacula-sd.conf like:

Device {
   Name = "xf1-contaboS3-dev"
   MediaType = "cloudS3-media"
   DeviceType = "Cloud"
   ArchiveDevice = "/backup/cloud"
   RemovableMedia = no
   RandomAccess = yes
   Autochanger = yes
   MaximumFileSize = 2097152
   MaximumPartSize = 2097152
   Cloud = "contabo-bucket1"
}
Cloud {
   Name = "contabo-bucket1"
   Driver = "S3"
   HostName = "eu2.contabostorage.com"
   BucketName = "bucxxxx"
   AccessKey = "xxx"
   SecretKey = "xxxx"
   Protocol = "HTTPS"
}
Autochanger {
   Device = "xf1-contaboS3-dev"
   Name = "s3-changer"
   ChangerCommand = "/opt/bacula/scripts/mtx-changer %c %o %S %a %d"
   ChangerDevice = "/dev/null"
}

The changer doesn't show up in bacularis, I add it in the API menu and 
get things like "/dev/null is not an sg device, or old sg driver". Sure.

What else to use there?

I browse the ml archive for examples etc

What I would like to have:

An Autochanger that writes to N "tapes" in that bucket, for sure 
encrypted ...

pls advise, I am a bit lost

I read 
https://docs.baculasystems.com/BEDedicatedBackupSolutions/StorageBackend/cloud/cloud-backup.html 
for now ...