Encryption is key for securing your data. Utilize tools such as VeraCrypt and Cryptomator for robust file encryption prior to uploading them to cloud storage. Alternatively, consider using virtual tapes, as implemented by Starwind VTL. In this caseour data remains unaccessible to cloud providers.
As others said, Rclone and encrypt your data before sending. I wouldn't trust no matter what the cloud provider says.
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.